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Research Article
Phylogeny and classification of the Australasian and Indomalayan mimosoid legumes Archidendron and Archidendropsis (Leguminosae, subfamily Caesalpinioideae, mimosoid clade)
expand article infoGillian K. Brown§, Javier Aju|, Michael J. Bayly, Daniel J. Murphy, Todd G. B. McLay
‡ University of Melbourne, Parkville, Australia
§ Queensland Herbarium, Department of Environment and Science, Toowong, Australia
| Universidad del Valle de Guatemala, Guatemala, Guatemala
¶ National Herbarium of Victoria, Royal Botanic Gardens Victoria, South Yarra, Australia
Open Access

Abstract

The morphologically variable genus Archidendron is the second largest mimosoid legume genus from the Indomalayan-Australasian region, yet it has not been well represented in phylogenetic studies. Phylogenies that have included multiple representatives of Archidendron suggest it may not be monophyletic, and the same applies to Archidendropsis, another understudied genus of the Archidendron clade. The most comprehensive phylogeny of Archidendron and Archidendropsis to date is presented, based on four nuclear markers (ITS, ETS, SHMT and RBPCO). Exemplars from all genera of the wider Archidendron clade are sampled, including representatives of all series within Archidendron and the two subgenera of Archidendropsis. Our results confirm that Archidendron and Archidendropsis are not monophyletic. Within Archidendron, only one series (ser. Ptenopae) is resolved as monophyletic and species of Archidendron are divided into two primarily geographic lineages. One clade is distributed in western Malesia and mainland Asia and includes most representatives of series Clypeariae, while the other is mostly restricted to eastern Malesia and Australia and includes representatives of the seven other series plus two samples of series Clypeariae. No taxonomic changes are made for Archidendron due to the high level of topological uncertainty and the lack of discrete macromorphological characters separating these two lineages. Each of the two subgenera of Archidendropsis is monophyletic but they are not closely related. A new genus endemic to Queensland (Australia), Heliodendron Gill.K. Br. & Bayly, gen. nov., is described for the former Archidendropsis subg. Basaltica, and combinations for its three species are proposed: Heliodendron basalticum (F. Muell.) Gill.K. Br. & Bayly, comb. nov., Heliodendron thozetianum (F. Muell.) Gill.K. Br. & Bayly, comb. nov., and Heliodendron xanthoxylon (C.T. White & W.D. Francis) Gill.K. Br. & Bayly, comb. nov.

Keywords

Fabaceae, ingoid clade, legumes, low copy nuclear gene, Malesia, phylogeny, targeted amplicon sequencing

Introduction

The classification of mimosoid legumes has been significantly transformed in the past 20 years since the first comprehensive molecular phylogeny of the then subfamily Mimosoideae (Luckow et al. 2003). Understanding of relationships within the mimosoid legumes has improved through studies at generic, regional, alliance, subfamilial and familial levels (see references in Legume Phylogeny Working Group 2017; Koenen et al. 2020; Ringelberg et al. 2022). In the comprehensive phylogeny and revision of the legume family (Leguminosae or Fabaceae), the mimosoid legumes formed a clade nested within the re-circumscribed subfamily Caesalpinioideae (Legume Phylogeny Working Group 2017). Recent phylogenomic data have sufficiently enhanced resolution to enable recognition of several clades within subfamily Caesalpinioideae, including the mimosoid, core mimosoid and ingoid clades (Koenen et al. 2020; Ringelberg et al. 2022). However, within these clades some large genera, such as Archidendron F. Muell. and allies have remained under-studied relative to Acacia Mill. s.l. and many Neotropical ingoid genera and groups (e.g. Murphy et al. 2010; de Souza et al. 2013; Iganci et al. 2016; Miller et al. 2017; Ferm et al. 2019; Comben et al. 2020).

The two largest mimosoid genera from the Indomalayan-Australasian region are Acacia and Archidendron. These are placed in the Archidendron clade (sensu Koenen et al. 2020), along with Archidendropsis I.C. Nielsen, Falcataria (I.C. Nielsen) Barneby & J.W. Grimes, Pararchidendron I.C. Nielsen, Paraserianthes I.C. Nielsen, Serianthes Benth. and Wallaceodendron Koord. The Archidendron clade is biogeographically distinct within the mimosoid legumes, being primarily restricted to the Indomalayan and Australasian regions, and has been given several names over the years to reflect this: the Australian & SE Asian Ingeae clade (Brown et al. 2008) and the Australo-Malesian mimosoids (Brown et al. 2011). Within the Archidendron clade, Pararchidendron, Paraserianthes and Wallaceodendron are monotypic, and three of the other five genera (Acacia s.s., Falcataria, and Serianthes) are well documented as monophyletic based on morphological and genetic data (Chappill and Maslin 1995; Miller and Bayer 2001; Luckow et al. 2003; Brown et al. 2008, 2011; Murphy et al. 2010; Demeulenaere et al. 2022; Ringelberg et al. 2022). However, Archidendron has been suggested to be paraphyletic (Brown et al. 2008, 2011; Iganci et al. 2016; Demeulenaere et al. 2022; Ringelberg et al. 2022), as has Archidendropsis (Demeulenaere et al. 2022; Ringelberg et al. 2022).

Archidendron is the second largest genus in this clade after Acacia, with 99 described species and an additional 20 putative species that are poorly known due to limited collections or destroyed types (Nielsen et al. 1984b; Cowan 1998; Wu and Nielsen 2010; Dash and Sanjappa 2011). They are small to medium-sized trees found in lowland and montane tropical and subtropical rainforests of the Australo-Malesian and Pacific regions, distributed from Kerala (southern India) and Sri Lanka in the west, to the Solomon Islands in the east; and from Taiwan and the Ryukyu Islands in the north, to Australia in the south (Fig. 1; Nielsen et al. 1984b, 1984a). In the 1970s and 1980s, an extensive revision of the Australo-Malesian and Pacific Ingeae was undertaken (Nielsen 1979, 1981, 1982; Nielsen et al. 1983b, 1983a, 1984b) and Archidendron was expanded based on evidence from wood, pollen, seed and inflorescence characteristics to include species previously referred by Kostermans (1954) to the genera Abarema Pittier, Cylindrokelupha Kosterm., Morolobium Kosterm., Paralbizzia Kosterm., Zygia P. Browne, and by Bentham (1875) to Pithecellobium sect. Clypearia sensu Benth. (Baretta-Kuipers 1981; Nielsen et al. 1984b; Nielsen 1992). Archidendron now includes unarmed trees or shrubs with bipinnate leaves, mostly opposite leaflets, extrafloral nectaries, and wood anatomy of strictly uniseriate rays and abundant parenchyma with a banded distribution (Nielsen et al. 1984b).

Figure 1. 

Distribution maps of the genera Archidendron and Archidendropsis. The maps are based on quality-controlled species-level digitised herbarium specimens from GBIF (www.gbif.org) (Ringelberg et al. 2022). Maps were created using R packages ggplot2 (Wickham 2016), sf (Pebesma 2018), and rnaturalearth (South 2017) A Archidendron. Species distributions are coloured according to the ncDNA phylogeny clades (Fig. 2) except for A. clypearia: Clade E (Clypeariae clade) = green dots; clade F (Archidendron s.s. clade) = blue dots; species not sampled for the phylogeny = red dots. Archidendron clypearia is widespread and falls in both clades E and F, so for this species locations of samples in the ncDNA phylogeny are coloured according to their clade and all other records of this species are coloured red. The overall distribution of series Clypeariae is shown by a blue dashed line B Archidendropsis. All species that belong to subg. Archidendropsis are coloured red and those in subg. Basaltica (= Heliodendron gen. nov.) are coloured orange.

Archidendron is morphologically variable especially in leaf, inflorescence, flower, and pod characteristics, and has been divided into eight series (Nielsen et al. 1984b): Clypeariae (Benth.) I.C. Nielsen, Archidendron, Calycinae I.C. Nielsen, Bellae I.C. Nielsen, Ptenopae I.C. Nielsen, Pendulosae (Mohlenbr.) I.C. Nielsen, Stipulatae (Mohlenbr.) I.C. Nielsen and Morolobiae (Kosterm.) I.C. Nielsen. The largest series, Clypeariae (ca. 51 species) is distributed in mainland southeast Asia, western Malesia, and the Philippines, with only a few species found further east (Fig. 1A). This series is well defined by the absence of stipules and flowers that generally have one carpel per ovary that is often stipitate (Nielsen et al. 1984b). The second largest series, Archidendron (ca. 15 species), is found in eastern Malesia and Australia and is defined by the presence of stipules and stipular glands. Four of the series are largely confined to the island of New Guinea (Nielsen et al. 1984b): series Calycinae (3 species) with strongly ribbed inflated calyces, cauliflorous racemes and sessile ovaries; series Bellae (4 species) with large woody pods without overgrown seeds and cauliflorous paniculate inflorescences; series Ptenopae (2 species), which is defined by the presence of two-winged rachises and pinnae; series Pendulosae (3 species) have inflorescences with lax racemes (Nielsen et al. 1984a). Series Stipulatae (ca. 14 species) are found in New Guinea, the Moluccas, and Queensland (Australia) and have floral bracts with extra floral nectaries, stipular glands and cauliflorous branched racemes (Nielsen et al. 1984b). The three species of series Morolobiae have unifoliolate pinnae, and racemose inflorescences with flowers with single, sessile ovaries, and are disjunctly distributed: A. monopterum (Kosterm.) I.C. Nielsen in Halmahera (North Maluku Islands, Indonesia), A. whitei I.C. Nielsen in northern Queensland (Australia) and A. muellerianum (Maiden & R.T. Baker) I.C. Nielsen in northern New South Wales (Australia) (Nielsen et al. 1984b).

Prior to resolution of the Archidendron clade, the genus Archidendron was suggested to be related to taxa of the Inga-alliance (Barneby and Grimes 1996; Lewis and Rico Arce 2005) or to other Old World genera, such as Archidendropsis, Falcataria, Pararchidendron, Paraserianthes and Serianthes (Baretta-Kuipers 1981; Nielsen et al. 1984a; Nielsen 1992). Archidendron has not been well represented in molecular phylogenies to date with only ten of the 99 species and four of the eight series (Archidendron, Clypeariae, Morolobiae and Ptenopae) included in any one study. In all studies, samples of series Clypeariae are placed distantly from the other series (Brown et al. 2008, 2011; Iganci et al. 2016; Koenen et al. 2020; Demeulenaere et al. 2022; Ringelberg et al. 2022).

The genus Archidendropsis includes 14 species from New Caledonia, the Solomon Islands, New Britain, Papua New Guinea and Australia (Fig. 1B), with all species endemic to their respective region (Nielsen et al. 1983a). Species of Archidendropsis have winged, thin-walled seeds lacking a pleurogram (a mark or depression on both sides of the seed coat; Rodrigues-Junior et al. 2021) and are placed in two subgenera based on pollen and inflorescence characteristics. Species of subgenus Basaltica I.C. Nielsen are restricted to Australia, have smaller polyads (55–60 μm) and globular inflorescences, while species of subgenus Archidendropsis are not found in Australia, have larger polyads (80–120 μm) and flowers arranged in spicate racemes. Like Archidendron, Archidendropsis has been poorly represented in molecular phylogenies with only one or two of the 14 species included in any one study (Brown et al. 2008, 2011; Ferm et al. 2019; Koenen et al. 2020; Demeulenaere et al. 2022; Ringelberg et al. 2022). Only two studies have included representatives of each of the subgenera and in both, Archidendropsis is not resolved as monophyletic (Demeulenaere et al. 2022; Ringelberg et al. 2022).

This study aims to test the monophyly of the genera Archidendron and Archidendropsis and investigate phylogenetic relationships within the large genus Archidendron to test the monophyly of its infrageneric series.

Materials and methods

Taxon sampling and DNA isolation

A total of 87 accessions were sampled, representing 43 species of Archidendron (68 accessions), five species of Archidendropsis (six accessions) and nine species (11 accessions) of the other genera in the Archidendron clade; two species of Old World Albizia Durazz. were included as outgroups (Table 1). In total 43% of the species of Archidendron were sampled including representatives of all eight series. Both subgenera of Archidendropsis were sampled covering 36% of species in the genus. Samples were collected in the field and from herbarium specimens sourced from AAU, BISH, BRI, CANB, CNS, KEP, KUN, L, NY, MEL and MELU (herbarium codes as per Thiers, updated continuously).

Table 1.

Linked data table of specimens sampled for phylogeny. Specimen accession number linking herbarium specimen to sample ID, taxon name with authorities, locality information and geocode (where available) as provided on the specimen/database. GenBank numbers are provided for each marker and where multiple alleles were identified for a specimen, the two GenBank numbers are separated by a semi colon. If the marker was not successfully sequenced for a particular specimen, then the GenBank field is left blank.

Preserved specimen Associated sequences Taxon name/MOTU Sample ID Location
Specimen code (InstCode and/or CollCode + Catalogue #) SHMT RBPCO ITS ETS trnK trnV psbD Geolocation name / locality GPS Coordinates
MEL 2294706A OM286906 OM286992 ON013654 Acacia baueri Benth. Z176 Great Sandy National Park, Fraser Island, Woralie track to Moon Point. Queensland, Australia 153°11'55"E, 25°11'38"S
MELU GB309b OM984488 OM390190; OM390191 OM286907 OM286993 ON013655 ON101510 OM984574 Acacia myrtifolia (Sm.) Willd. JA150 0.7km north of Playford Highway on Snug Bay Rd, Kangaroo Island, South Australia 136°52'51.8"E, 35°46'30.2"S
CANB 864530.1 OM984489 OM286908 OM286994 ON013656 ON101511 OM984575 Albizia lebbeck (L.) Benth. JA137 Alva, NE of Ayr, Queensland, Australia 147°28'52"E, 19°27'11"S
MEL 2391890A OM984490 OM286909 OM286995 ON013657 ON101512 OM984576 Albizia retusa Benth. Z106 Atherton Arboretum. Tag #96. Queensland, Australia 145°29'8.6"E, 17°15'31.4"S
KUN0599506 OM984491 OM286910 OM286996 ON013658 ON101513 OM984577 Archidendron alternifoliolatum (T.L.Wu) I.C.Nielsen JA25 China 100.85°E, 24.5667°N
BRI AQ0380081 OM984492; OM984493 OM286911 OM286997 ON013659 ON101514 Archidendron arborescens (Kosterm.) I.C.Nielsen JA36 Papua New Guinea, Western Fly; Kwinja Lakes area of the Middle Fly River 141°41'33.987"E, 7°45'24.772S
KUN0599551 OM984494; OM984495 OM286912 OM286998 ON013660 ON101515 Archidendron balansae (Oliv.) I.C.Nielsen JA26 China
AAU D.McKey92-9 OM984496; OM984497 OM390192 OM286913 OM286999 ON013661 ON101516 OM984578 Archidendron bigeminum (L.) I.C.Nielsen JA14 Sinharaja Forest, SW Sri Lanka 80°35'23"E, 6°21'17"N
AAU Balgooy6063 OM984498; OM984499 OM390193 OM286914 OM287000 ON013662 ON101517 OM984579 Archidendron borneense (Benth.) I.C.Nielsen JA70 Tanah Merah, Kalimantan Timur 117°‘E, 1°‘S
KEP FRI53789 OM984500; OM984501 OM286915 OM287001 ON013663 ON101518 OM984580 Archidendron bubalinum (Jack) I.C.Nielsen JA22 Pahang, Temerloh, Tasik Bera, Kg. Patihir, Malaysia 102.4167°E, 3.8167°N
CANB 730419.1 OM390194; OM390195 OM286916 OM287002 ON013664 ON101519 Archidendron calliandrum de Wit JA109 Ambunti District, Waskut Hills, spur ridge NW of Musapien bivouac. East Sepik, PNG 142°43'55"E, 4°10'36"S
CANB 211609.1 OM984502 OM286917 OM287003 ON013665 ON101520 OM984581 Archidendron calycinum Pulle JA129 Saw Mountains, near junction of Tauri and Kapau Rivers. Gulf Province, PNG 146°8'E, 7°47'S
AAU L.Averyanov4481 OM984503 OM286918 OM287004 ON013666 ON101521 OM984582 Archidendron chevalieri (Kosterm.) I.C.Nielsen JA71 Bi Dup ridge, Vietnam 108°39'E, 12°6'N
AAU I.Nielsen26 OM984504 OM286919 OM287005 ON013667 ON101522 OM984583 Archidendron clypearia (Jack) I.C.Nielsen JA16 Gunung Mulu National Park, Sarawak 114°55'E, 4°05'N
AAU H.M.Christensen38 OM984505 OM286920 OM287006 ON013668 ON101523 OM984584 Archidendron clypearia (Jack) I.C.Nielsen JA05 Pa Dalih area, Sarawak 115°50'E, 3°40'N
AAU L.AveryanovVH3188 OM984506 OM286921 OM287007 ON013669 ON101524 OM984585 Archidendron clypearia (Jack) I.C.Nielsen JA15 Bi Dup mountain system, Vietnam 108°39'E, 12°8'N
CANB 525617.1 OM984507 OM390196; OM390197 OM286922 OM287008 ON013670 ON101525 OM984586 Archidendron clypearia (Jack) I.C.Nielsen JA95 East branch of the Avi Avi River. Gulf Province, PNG 146°30'E, 7°44'S
AAU AmbriW838 OM286923 OM287009 ON013671 ON101526 OM984587 Archidendron cockburnii I.C.Nielsen JA17 Wanariset research area, Kalimantan Timur 117°‘E, 1°‘S
NY03986843 OM390198 OM286924 OM287010 ON013672 ON101527 OM984588 Archidendron contortum (Mart.) I.C.Nielsen T97 Near Kuala Lumpur, Malaysia
BRI AQ0380332 OM286925 OM287011 Archidendron forbesii Baker f. JA38 Papua New Guinea, Central; Subitana, Sogeri sub-dist., Central, Papua 147°31'E, 9°25'S
BISH752370 OM984509 OM390199 OM286926 OM287012 ON013673 ON101528 OM984589 Archidendron glabrum (K.Schum.) Lauterb. & K.Schum. JA04 Siboma, Sayama, track along the ridgeline S from Camp 1. PNG 147.298°E, 7.52857°S
BISH763497 OM984510 OM390200 OM286927 OM287013 ON013674 ON101529 OM984590 Archidendron glabrum (K.Schum.) Lauterb. & K.Schum. JA115 Morobe Province; Oomsis, behind PNG Forestry station. 146.821°E, 6.71325°S
BRI AQ0380375 OM286928 OM287014 ON013675 ON101530 OM984591 Archidendron glandulosum Mohlenbr. ex Verdc. JA39 Brown River F.R. Central Province, PNG 147°10'33.78"E, 9°30'24.60"S
AAU J.F.Maxwell82-141 OM984511 OM286929 OM287015 ON013676 ON101531 OM984592 Archidendron globosum (Blume) I.C.Nielsen JA20 Near Bukit Kallang, Singapore
AAU Bjornland445 OM984512 OM286930 OM287016 ON101532 OM984593 Archidendron glomeriflorum (Kurz) I.C.Nielsen JA10 Chiang Mai: Amphoe Muang, Mae Rim, Thailand
CANB 544379.1 OM984516 OM286933 OM287018 ON013679 ON101535 OM984596 Archidendron grandiflorum (Sol. ex Benth.) I.C.Nielsen JA100 Gabba Island, Torres Strait. Queensland, Australia 142°38'22"E, 9°46'8"S
BRI AQ0814833 OM984513; OM984514 OM286931 OM287017 ON013677 ON101533 OM984594 Archidendron grandiflorum (Sol. ex Benth.) I.C.Nielsen JA42 Curramore Sanctuary Nature Reserve, 14km NW of Maleny. Queensland, Australia 152°4'05"E, 26°41'43"S
CNS 131336.1 OM984515 OM286932 ON013678 ON101534 OM984595 Archidendron grandiflorum (Sol. ex Benth.) I.C.Nielsen JA43 Mt Lewis, Carbine Tableland. Queensland, Australia 145°16'E, 16°31'S
MEL 2391892A OM984517; OM984518 OM390201 OM286934 OM287019 ON013680 ON101536 OM984597 Archidendron grandiflorum (Sol. ex Benth.) I.C.Nielsen Z109 Atherton Arboretum. Tag #846. Queensland, Australia 145°29'8.6"E, 17°15'31.4"S
AAU Kostermans22121 OM286935 OM287020 ON013681 ON101537 Archidendron harmsii Malm JA74 Mbengen, West Flores
AAU H.M.Christensen279 OM984519 OM390202; OM390203 OM286936 OM287021 ON013682 ON101538 OM984598 Archidendron havilandii (Ridl.) I.C.Nielsen JA75 Pa Dalih area, Sarawak 115°50'E, 3°40'N
CANB 596487.1 OM984521 OM390206 OM286939 OM287024 ON013685 ON101541 OM984600 Archidendron hendersonii (F.Muell.) I.C.Nielsen JA103 Greenfield Road, Lennox Head. New South Wales, Australia 153°36'E, 28°49'’S
MEL 2293327A OM984520 OM390204; OM390205 OM286937 OM287022 ON013683 ON101539 OM984599 Archidendron hendersonii (F.Muell.) I.C.Nielsen JA44 Brandy Creek Road, 9 km S of Airlie Beach. Queensland, Australia 148°43'15"E, 20°21'2"S
QRS 18805.2 OM286938 OM287023 ON013684 ON101540 Archidendron hendersonii (F.Muell.) I.C.Nielsen JA45 Between Starcke homestead and Starcke River. Queensland, Australia 145°5'E, 14°55'S
MEL 2391969A OM984522 OM390207; OM390208 OM286940 OM287025 ON013686 ON101542 OM984601 Archidendron hendersonii (F.Muell.) I.C.Nielsen Z114 Cairns, cultivated in garden. Queensland, Australia 145°46'15"E, 16°55'13"S
QRS 117169.1 OM984523 OM390209 OM286941 OM287026 ON013687 ON101543 OM984602 Archidendron hirsutum I.C.Nielsen JA46 Claudie River. Queensland, Australia 143°15'E, 12°44'S
CNS 142441.1 OM984524 OM390210 OM286942 OM287027 ON013688 ON101544 OM984603 Archidendron hirsutum I.C.Nielsen JA86 Umagico, Cape York. Queensland, Australia 142°21'E, 10°53'19"S
MEL 2391887A OM984525 OM390211 OM286943 OM287028 ON013689 ON101545 OM984604 Archidendron hirsutum I.C.Nielsen Z113 Atherton Arboretum. Tag #482. Queensland, Australia 145°29'8.6"E, 17°15'31.4"S
BISH760310 OM984526 OM390212 OM286944 OM287029 ON013690 ON101546 OM984605 Archidendron hispidum (Mohlenbr.) Verdc. JA02 Northern Province; Sibium Mountains; W of Akupe Camp, along Afase River. PNG 148.269°E, 9.28974°S
AAU R.Geesink7254 OM984527 OM286945 OM287030 ON013691 ON101547 OM984606 Archidendron jiringa (Jack) I.C.Nielsen JA12 Kao Chong Botanical Garden, Thailand 99°45'E, 7°40'N
BRI AQ0738090 OM984528; OM984529 OM390213 OM286946 OM287031 ON013692 ON101548 OM984607 Archidendron kanisii R.S.Cowan JA47 Oliver Creek. Queensland, Australia 145°26'E, 16°8'S
MELUD113392a OM984530 OM286947 OM287032 ON013693 ON101549 OM984608 Archidendron kanisii R.S.Cowan JA65 Shore of creek, end of Stonewood Road, Queensland, Australia 145.40497°E, 16.16685°S
MELUD113385a OM984531 OM390214 OM286948 OM287033 ON013694 ON101550 OM984609 Archidendron kanisii R.S.Cowan JA66 Shore of creek, end of Stonewood Road, Queensland, Australia 145.40497°E, 16.16685°S
BRI AQ0733240 OM984532 Archidendron kanisii R.S.Cowan Z49 NPR133, Daintree, Oliver Creek, Queensland, Australia 145°26'29.997"E, 16°8'11.708"S
AAU I.Cowley110 OM286949 OM287034 ON013695 ON101551 OM984610 Archidendron kinabaluense (Kosterm.) I.C.Nielsen JA76 Melilas. Ulu Belait, Brunei
AAU H.M.Christensen1719 OM286950 OM287035 ON013696 ON101552 OM984611 Archidendron kunstleri (Prain) I.C.Nielsen JA07 near Nanga Sumpa, Sarawak 112°10'E, 1°20'N
KUN 0599659 OM984533; OM984534 OM390215 OM286951 OM287036 ON013697 ON101553 OM984612 Archidendron laoticum (Gagnep.) I.C.Nielsen JA77
BRI AQ0835639 OM984535 OM286952 OM287037 ON013698 ON101554 Archidendron lovelliae (F.M.Bailey) I.C.Nielsen JA48 Great Sandy National Park; Cooloola Section, Freshwater Road. Queensland, Australia. 153°6'52"E, 25°57'01S
BRI AQ0636343 OM390216; OM390217 OM286953 OM287038 ON013699 ON101555 OM984613 Archidendron lovelliae (F.M.Bailey) I.C.Nielsen Z112 Harry’s Hut Road, Cooloola National Park.Queensland, Australia 153°03'E, 25°26'S
MEL 2034578A OM984536 OM390218; OM390219 OM286954 OM287039 ON013700 ON101556 OM984614 Archidendron lucyi F.Muell. JA49 Indooroopilly, cultivated. Queensland, Australia
MELUD113387a OM984537 OM286955 OM287040 ON013701 ON101557 OM984615 Archidendron lucyi F.Muell. JA62 Lake Road near Cairns, Queensland, Australia 145.6693°E, 16.875165°S
MELUD113393a OM984538 OM286956 OM287041 ON013702 ON101558 OM984616 Archidendron lucyi F.Muell. JA63 Lake Road near Cairns, Queensland, Australia 145.6693°E, 16.875165°S
MELUD113391a OM984539 OM286957 OM287042 ON013703 ON101559 OM984617 Archidendron lucyi F.Muell. JA68 Cape Tribulation Road, adjacent to Coconut Beach resort, Queensland, Australia 145.45726°E, 16.11345°S
MEL 2391968A OM984540 OM390220 OM286958 OM287043 ON013704 ON101560 OM984618 Archidendron lucyi F.Muell. Z108 Cairns, cultivated in garden. Queensland, Australia 145°46'15"E, 16°55'13"S
BISH760584 OM984541 OM286959 OM287044 ON013705 ON101561 OM984619 Archidendron megaphyllum Merr. & L.M.Perry JA03 Central Province; Mt Gerebu, trail towards summit ridge. PNG 147.646°E, 9.46595°S
AAU H.M.Christensen1282 OM286960 OM287045 ON101562 OM984620 Archidendron microcarpum (Benth.) I.C.Nielsen JA06 Near Sumpa, Sarawak. 112°10'E, 1°20'N
BRI AQ0499073 OM984544 OM390221; OM390222 OM286962 OM287047 ON013707 ON101564 OM984622 Archidendron muellerianum (Maiden & R.T.Baker) I.C.Nielsen JA112 Big Scrub Flora Reserve, NNE of Lismore, New South Wales, Australia 153°19'44.880"E, 28°38'18.228"S
BRI AQ0763292 OM984542; OM984543 OM286961 OM287046 ON013706 ON101563 OM984621 Archidendron muellerianum (Maiden & R.T.Baker) I.C.Nielsen JA50 Tallebudgera Creek Road, reveg site. Queensland, Australia 153°21'57"E, 28°10'37"S
BISH752405 OM984545; OM984546 OM390223 OM286963 OM287048 ON013708 ON101565 OM984623 Archidendron parviflorum Pulle JA01 Morobe Province; Siboma, Sayama, above Sayama Creek, to E Camp 1. PNG 147.302°E, 7.52557°S
MEL 2074350A OM286964 OM287049 ON013709 Archidendron pellitum (Gagnep.) I.C.Nielsen JA34 N. de Dalat, prov. Ht. Donnai. Indochina: Annam. Vietnam 108°27'E, 11°57'N
Bell Museum 913425 (WP-3A0575) OM984547; OM984548 OM390224 OM286965 OM287050 ON013710 ON101566 OM984624 Archidendron ptenopum Verdc. JA116 Wanang village, Madang, PNG 145°10.631'E, 5°14.238'S
AAU C.Charoenphol5025 OM984549; OM984550 OM286966 OM287051 ON013711 ON101567 OM984625 Archidendron quocense (Pierre) I.C.Nielsen JA13 Ko Rang Yai, Thailand 102°23'E, 11°48'N
MEL 2391884A OM984557 OM390228 OM286969 OM287053 ON013717 ON101573 OM984630 Archidendron ramiflorum (F.Muell) Kosterm. Z111 Atherton Arboretum. Tag #1652. Queensland, Australia 145°29'8.6"E, 17°15'31.4"S
MELUD113388a OM984551 OM286967 OM287052 ON013712 ON101568 OM984626 Archidendron ramiflorum (F.Muell) Kosterm. JA67 Regeneration plot, Daintree Rainforest Observatory, Queensland, Australia 145.45004°E, 16.10268°S
BRI AQ0485087 OM390225 OM286968 Archidendron ramiflorum (F.Muell) Kosterm. Z110 Shiptons Flat. Queensland, Australia 145°14'E, 15°47'S
AAU Balgooy6769 OM984552 OM390226 OM286970 OM287054 ON013713 ON101569 Archidendron sp. nov. in obs. JA85 Pulan Baun, Aru Island Indonesia 134°35'E, 6°30'S
BRI AQ0052837 OM984553; OM984554 OM286971 OM287055 ON013714 ON101570 OM984627 Archidendron syringifolium (Kosterm.) I.C.Nielsen JA41 Agu River branch of the middle Fly River, PNG 141.166667°E, 6.966667°S
MEL 2041191A OM984555 OM390227 OM286972 OM287056 ON013715 ON101571 OM984628 Archidendron vaillantii (F.Muell) F.Muell. JA51 Cape Tribulation, Queensland, Australia 145°27'E, 16°6'15"S
BRI AQ0558405 OM984556 OM286973 OM287057 ON013716 ON101572 OM984629 Archidendron vaillantii (F.Muell) F.Muell. JA52 Along Paluma Dam Road, Ethel Creek, Queensland, Australia 146°10'40.222"E, 19°0'7.863"S
MEL 2196304A OM984558 OM286974 OM287058 ON013718 ON101574 OM984631 Archidendron whitei I.C.Nielsen JA53 State Forest 310 Gadgarra. Queensland, Australia 145°43'26"E, 17°18'13"S
BRI AQ0824396 OM390229 OM286975 OM287059 ON013719 ON101575 OM984632 Archidendron whitei I.C.Nielsen JA54 7km W of Babinda, Queensland, Australia. 145°54'30"E, 17°20'30"S
KUN 0599686 OM984559; OM984560 OM286976 OM287060 ON013720 ON101576 OM984633 Archidendron xichouense (C.Chen & H.Sun) X.Y.Zhu JA84 China
BRI AQ0611431 OM286978 OM287062 ON013723 Archidendropsis basaltica (F.Muell.) I.C.Nielsen Z218 On Isaac River and Hill Creek. 25km S of Glenden, Queensland, Australia 148°7'E, 21°33'01"S
MEL 0290000A OM286977 OM287061 Archidendropsis basaltica (F.Muell.) I.C.Nielsen Z44 Bladensburg National Park, S of Winton, Poison Paddock. Queensland, Australia 143°2'23"E, 22°41'9"S
MEL 2333247A OM984561; OM984562 OM286979 OM287063 ON013721 ON101577 OM984634 Archidendropsis granulosa (Labill.) I.C.Nielsen Z362 Prov. Sud, near Yate, north side of Yate River. New Caledonia 166°56'0"E, 22°9'29"S
BRI AQ0430532 OM286980 OM287064 ON013724 Archidendropsis lentiscifolia (Benth.) I.C.Nielsen Z122 c. 5km north of Kone, south of Kafeate. New Caledonia. 164.78333°E, 21.05°S
MEL 2095888A OM286981 OM287065 ON013725 ON101578 OM984635 Archidendropsis thozetiana (F.Muell.) I.C.Nielsen JA144 Palmgrove National Park, 5km W of Daydream Hill, Queensland, Australia 149°13'29"E, 24°59'3"S
BRI AQ0771148 OM286982 OM287066 ON013722 Archidendropsis xanthoxylon (C.T.White & W.D.Francis) I.C.Nielsen Z121 Daintree, narrow ridge above Cassowary Creek, off Stewart Creek road, site 69. Queensland, Australia 145°17'46"E, 16°17'56"S
L.1958248 OM984563 OM390230 OM286983 OM287067 ON013726 ON101579 OM984636 Falcataria moluccana (Miq.) Barneby & J.W.Grimes JA134 KPC area, Sebongkok Utara, East Kalimantan, Indonesia. 117°31'59"E, 0°48'0"N
CANB 367091.1 OM984564 OM390231 OM286984 OM287068 ON013727 ON101580 OM984637 Falcataria toona (F.M.Bailey) Gill.K.Br., D.J.Murphy & Ladiges JA149 Near Earlando, 27 km N of Proserpine. Queensland, Australia 148°33'E, 20°10'S
MEL 1615244A OM984567 OM390234; OM390235 OM286987 OM287071 ON013730 OM984640 Pararchidendron pruinosum (Benth.) I.C.Nielsen Z50 Palm Tree Creek, W of Mt Whitestone township, Queensland, Australia 152°4'E, 27°39'S
CNS 134531.1 OM984565 OM390232 OM286985 OM287069 ON013728 ON101581 OM984638 Pararchidendron pruinosum (Benth.) I.C.Nielsen JA55 CSIRO Arboretum, Queensland, Australia 145°29'6"E, 17°15'28"S
QRS 121813.1 OM984566 OM390233 OM286986 OM287070 ON013729 ON101582 OM984639 Pararchidendron pruinosum (Benth.) I.C.Nielsen JA56 Clarke Range, Queensland, Australia 148°31'E, 21°16'S,
MEL 2183015A OM984568; OM984569 OM390236 OM286988 OM287072 ON013731 ON101583 OM984641 Paraserianthes lophantha (Willd.) I.C.Nielsen Z43 Merrimu Reservoir, Victoria, Australia 144°29'23"E, 37°38'3"S
BRI AQ0408829 OM984570; OM984571 OM390237 OM286989 OM287073 ON013732 ON101584 OM984642 Serianthes nelsonii Merr. JA143 Atop Sailigai Hulo, Rota. Northern Mariana Islands. 145°12'53"E, 14°09'03"N
MEL 2333248A OM984572 OM390238 OM286990 OM287074 ON013733 ON101585 OM984643 Serianthes petitiana Guillaumin Z361 Prov. Sud, near Prony, New Caledonia 166°49'52"E, 22°19'4"S
MELU SRA051 OM984573 OM390239 OM286991 OM287075 ON013734 ON101586 OM984644 Wallaceodendron cellebicum Koord. Z48 Bogor Botanic Gardens collection Accession: B19610136

Total genomic DNA (gDNA) was extracted following the CTAB method of Doyle and Doyle (1987) with modifications as per Shepherd and McLay (2011). Isolated gDNA was quantified with a NanoDrop 2000 (ThermoScientific) spectrophotometer and cleaned with a 2.4 M sodium acetate wash. Recalcitrant herbarium material that failed using the CTAB method was extracted using the AccuPrep Stool genomic DNA extraction kit (Bioneer) using the manufacturer’s protocol with some modifications suggested by Schuster (pers. comm.). Only 30 mg of leaf material was used instead of the recommended 100–200 mg. A total of 600 µl of stool lysis buffer (SL) was added to the extraction tube instead of 400 µl, the incubation step was increased to one hour in total, centrifugation was done for 10 minutes at step five, and to maintain equal volumes, 600 µl of binding buffer was added. Two consecutive washes were performed using buffer 1 (W1). The final elution was done by adding 160 µl total elution buffer in two steps (first 60 µl, and then 100 µl) instead of a single elution with 200 µl.

Marker selection, primer design and library preparation

Eight nuclear markers (low copy genes: AIGP, CYB6, Eif3E, SHMT, RBPCO, UDPG; nrDNA: ITS, ETS) and four chloroplast DNA intergenic spacer regions (trnK-matK, trnV-ndhC, psbD-trnT, trnL-rpl32) were assessed for variability between nine individuals spanning the series of Archidendron using Sanger sequencing.

PCR reagents, primers and cycling conditions are described in Suppl. material 1 (Johnson and Soltis 1994; Sun et al. 1994; Käss and Wink 1997; Baldwin and Markos 1998; Miller and Bayer 2001; Ariati et al. 2006; Choi et al. 2006; Shaw et al. 2007; Li et al. 2008). PCR products were visualised on a 1.5% agarose gel with Easy ladder I (Bioline) and cleaned with ExoSAP-IT (USB) as per the manufacturer’s protocol. The purified amplicons were sequenced on an AB3730xl sequencer (Thermo Scientific) at the Australian Genome Research Facility, Melbourne. Sequences were aligned in Geneious v.8.1.4 (Biomatters Ltd.) and assessed for variability between the samples. The most variable loci were then used in a targeted amplicon sequencing (TAS) approach (McLay et al. 2021), sequencing pooled amplicons on an Illumina MiSeq. For this, additional internal primers were designed for the five loci that had a total amplicon length greater than 500 bp, in order to produce shorter amplicons that could be fully sequenced using a 500-cycle sequencing kit. These primers were designed using Primer 3 v.2.3.4 (Rozen and Skaletsky 2000) implemented in Geneious v.8.1.4 (Biomatters Ltd.), selecting priming sites in conserved regions across the nine sequenced individuals.

Library preparation followed the two-step PCR process outlined in McLay et al. (2021). The first step used the region-specific primers to amplify each locus individually for each sample. Initial PCR reactions included 1 × MyTaq Buffer (Bioline), 1.2 µl of MgCl2 2.5 M (Bioline, 100 mg mL), 1.2 µl of dimethyl sulfoxide (DMSO, 99.5%; Sigma-Aldrich), 3 µl of each “tailed” primer (10 µM), 0.375 U of MyTaq (Bioline), 100 ng of gDNA, and ultra-pure water to make up for 16 µl volume. Variations in these reactions are noted in Suppl. material 1 for specific loci. Conditions for PCR were based on those of Choi et al. (2006), Shaw et al. (2007), and Ariati et al. (2006) with modifications as required to obtain successful amplifications (Suppl. material 1). To estimate amplicon concentration to decide the volume of PCR product for amplicon pooling, 2.2 µl of PCR product and 2.5 µl of molecular ladder (Easyladder I, Bioline) were run on 1.5% agarose. A total of 120 ng of each nuclear DNA (ncDNA) region PCR product and 20 ng of each chloroplast region PCR product were pooled in the same well of a 96-well plate. The ncDNA were pooled in a higher concentration to account for the possible presence of different alleles. Pooled samples were cleaned with 1.5 × Serapure beads (Rohland and Reich 2012).

The second step used qPCR to add unique Illumina indexing barcodes to each sample for the pooled amplicons. Indexing PCR reactions consisted of 5 µM of each of index primer (McLay et al. 2021), 3 µl of pooled amplicons, 1 × Kapa HiFi ReadyMix (Biosystems) and ultra-pure water to make up a total of 25 µl reaction. Conditions for PCR were 95 °C for 1 min, followed by 13 cycles of 98 °C for 50 sec, 67 °C for 50 sec, and 72 °C for 20 sec, and a final extension at 72 °C for 30 sec. Each sample was then cleaned with 1.4 × Serapure beads and concentrations were quantified using fluorescence in a EnSpire multimode plate reader. In total, 10 ng of each indexed and cleaned sample was pooled together. The final pooled library was cleaned with 1.5 × Serapure bead-to-sample ratio and the library was submitted to the Australian Genome Research Facility, Melbourne for sequencing on an Illumina MiSeq using a 500 cycle MiSeq v2 Nano Kit.

Data analysis

Sequences obtained by Sanger sequencing were aligned by individual locus in Geneious v.8.1.4 (Biomatters Ltd.) and a consensus sequence was generated and used as the reference for the reads obtained by TAS. The demultiplexed TAS Illumina MiSeq files were imported into Geneious v.8.1.4. Reads were trimmed to remove adapters and low-quality sequence. The map-to-reference option was selected to map reads for each sample to the different reference loci using High Sensitivity/Medium settings and a minimum mapping quality of 20. A consensus sequence for each locus was generated for each individual with Generate Consensus Sequence (Threshold = 65%, with Ns called if coverage was less than 10). The forward and reverse reads of the low-copy nuclear genes (LCNG) overlapped so it was possible to phase these loci into separate alleles, but this was not possible for the nuclear ribosomal DNA loci (ETS and ITS) as the reads were not overlapping due to unexpected length variation in both of these loci. Alignments of individual consensus sequences for each locus were generated using MUSCLE (Edgar 2004) in Geneious v.8.1.4 and adjusted manually. For each LCNG, samples with multiple alleles were assessed for topological concordance between the different copies using neighbour-joining trees (using the Geneious tree-builder, HKY model) and NeighbourNet networks (SplitsTree4, default settings, Huson and Bryant 2006), to ensure that a conflicting signal was not introduced from distantly related allelic variants (see Suppl. material 2: SHMT network and tree and Suppl. material 3: RBPCO network and tree). Allelic variants within samples were largely concordant with one-another permitting consensus sequences for those samples to be used for subsequent phylogenetic analyses.

Alignments of all nuclear loci (ncDNA; with consensus sequences for LCNG alignments) were analysed individually to explore gene tree topologies in IQ-TREE v.1.6.12 on the web server (http://iqtree.cibiv.univie.ac.at/, Trifinopoulos et al. 2016) with support estimated with 1,000 ultra-fast bootstrap replicates (UFBS) (Minh et al. 2013). After comparing topologies, four ncDNA loci (ETS, ITS, RBPCO, SHMT) were concatenated into a single matrix as no major incongruencies were observed. The combined ncDNA dataset was partitioned into six partitions corresponding to each locus with the ITS region further divided in ITS1, 5.8S and ITS2 for subsequent analyses. IQ-TREE was used to perform maximum likelihood (ML) analyses on the concatenated ncDNA alignment. The analysis was run with the alignment partitioned and allowing ModelFinder (Kalyaanamoorthy et al. 2017) to identify the optimal substitution models for each partition (Table 2). Node support was estimated using 1,000 UFBS. Bayesian Inference (BI) was performed, with the alignment partitioned by locus. The best model of substitution for each partition was estimated with IQ-TREE model selection using the options: selection criteria of Bayesian (BIC), candidate models JC, F81, K80, HKY, SYM, GTR, heterogeneity types I, G, I+G, and the genomic source of nuclear (Table 2). MrBayes v.3.2.7a (Ronquist et al. 2012) was run using the CIPRES Science Gateway (Miller et al. 2010). Two parallel runs each with eight Monte Carlo Markov Chains were run for five million generations, sampling a tree every 1,000 generations and a burn-in of 25%.

A consensus network of the combined ncDNA dataset was constructed in SplitsTree4 (Huson and Bryant 2006) using the last 101 sampled BI trees (edge weights = mean, threshold = 0.05). This method allows for the visualisation of conflict in a set of trees and provides an alternative method of interpretation to a single fixed topology of a consensus tree.

Table 2.

ncDNA data partitions and best fit substitution models. Models estimated by IQ-TREE model selection and applied for BI.

Partition Model
ETS HKY+F+G4
ITS1 GTR+F+G4
5.8S SYM+I+G4
ITS2 HKY+F+G4
SHMT HKY+F+G4
RBPCO K2P+I

All chloroplast (cpDNA) loci were concatenated into a single matrix for phylogenetic analyses. IQ-TREE was used to perform ML analyses on the cpDNA matrix, with the alignment partitioned by locus, using ModelFinder to identify the optimal substitution model for each locus, and support was estimated using 1,000 UFBS replicates. The resulting topology was very poorly supported (though similar groups to the ncDNA phylogeny were discovered within the genus Archidendron). To further investigate cpDNA relationships within Archidendron, the outgroups were removed, and the IQ-TREE analysis was performed on the reduced dataset. The UFBS replicates were then used to create a consensus network in SplitsTree4 (edge-weights = mean, threshold = 0.20).

Pollen morphology of Archidendropsis subg. Basaltica

Pollen size and surface texture are key morphological features differentiating the subgenera of Archidendropsis but one of the three species of subg. Basaltica (A. xanthoxylon (C.T. White & W.D. Francis) I.C. Nielsen) was not examined by Nielsen et al. (1983b). To fill this gap and ensure consistency of results with published data, pollen from A. xanthoxylon (BRI AQ0199126, BRI AQ0874091, BRI AQ0199129 and BRI AQ0648303) and A. basaltica (F. Muell.) I.C. Nielsen (BRI AQ1003764, BRI AQ0199029, BRI AQ0625292 and BRI AQ0648454) of subg. Basaltica was examined. Pollen grains were obtained from flowers of herbarium specimens under a Zeiss dissecting microscope at the Queensland Herbarium (BRI) using clean forceps and a fine brush. Samples were mounted on aluminium stubs using double-sided carbon tabs and coated with gold using an Agar Scientific Automatic Sputter Coater. Pollen grains were observed and photographed using a Phenom G2 5keV (kiloelectron-volt) desktop scanning electron microscope (PhenomWorld). Pollen diameter for 10 grains of A. basaltica and eight grains of A. xanthoxylon was measured using ToupView (TOUPTEK PHOTONICS) software; overall fewer grains were available on specimens of A. xanthoxylon for microscopy.

Results

Targeted amplicon sequencing loci

Of the eight nuclear loci only four were included in the final phylogenetic analyses: SHMT, RBPCO, ITS and ETS. ETS and ITS amplified well, were variable, and are commonly used phylogenetic markers in Caesalpinioideae phylogenetic studies. Of the LCNGs, SHMT was the most informative, followed by RBPCO; allelic variation was found in some individuals for all LCNGs. Exploring allelic variation in the SHMT (36 samples with alleles) and RBPCO (24 samples with alleles) showed that for samples with more than one allele, the copies were closely related to each other (Suppl. material 2: SHMT network and tree and Suppl. material 3: RBPCO network and tree). Two LCNGs were excluded because few individuals of the target genera were successfully sequenced; only 12 sequences of Archidendron and two sequences of Archidendropsis were obtained for AlGP, and only 16 sequences of Archidendron and one Archidendropsis were obtained for Eif3E. The remaining two LCNG loci (CYB6 and UDPG) are not included in the analyses due to their short lengths, 240 bp and 202 bp respectively, and lack of variation.

Of the four chloroplast loci, trnK-matK was the most informative, followed by psbD-trnT and then trnV-ndhC. However, only one of the three blocks of trnV-ndhC was successfully sequenced. The internal primers designed allowed 100% coverage for the trnK-matK, 81% coverage for the psbD-trnT, and less than 30% coverage for the trnV-ndhC. It was not possible to obtain sequences for all samples for all blocks in which the three cpDNA regions were divided; as a result the cpDNA dataset was patchy. The trnL-rpl32 intergenic spacer did not amplify well, with 10 samples partially sequenced, and it was not included in final analyses.

Phylogenetic analyses

The topologies of the combined ncDNA Bayesian and IQ-TREE analyses were congruent (nodes supported with UFBS ≥ 95; PP ≥ 0.90) and the Bayesian tree is presented (Fig. 2A,B). The Archidendron clade was recovered as monophyletic (PP 1.0) with six well supported clades (A–F) resolved within it. However, the relationships between clades A–F were not well resolved or supported with a polytomy in the backbone of the phylogeny. Clade A (PP 0.99) includes all three species of Archidendropsis subg. Basaltica, clade B (PP 1.0) includes the three samples of Pararchidendron pruinosum (Benth.) I.C. Nielsen, and clade C (PP 1.0) includes the two sampled representatives of Archidendropsis subg. Archidendropsis. Four monophyletic genera are grouped together in clade D (PP 1.0), with Acacia sister to Paraserianthes in clade D1 (PP 1.0) and Falcataria sister to Serianthes (PP 1.0) in clade D2 (Fig. 2A). Clade E (PP 1.0) comprises all but two sampled representatives of Archidendron ser. Clypeariae, and all other samples of Archidendron are placed in clade F (PP 1.0). Clades C, D and Wallaceodendron are related (PP 0.98) and together are sister to Clade E (PP 0.96; Fig. 2A).

Figure 2. 

Combined ncDNA phylogeny of the Archidendron clade. The Bayesian Inference (BI) cladogram, phylogram, and consensus network for the combined ncDNA dataset are presented A Cladogram: the star indicates the Archidendron clade sensu Koenen et al. (2020). Nodes with PP = 1.0 are shown in bold while other nodes with PP ≥ 0.50 are noted under the node. Clades are labelled with letters above the node. Coloured bars to the right of clades are names discussed in the text. Nielsen’s series of Archidendron are shown as coloured circles next to the sample name; key to colour and series in legend B Phylogram: clades are labelled as per A and nodes with a PP = 1.0 are shown in bold C Consensus network: branches are colour coded and labelled as per the clades of A.

Within Archidendron, only one of Nielsen’s eight series is resolved as monophyletic (ser. Ptenopae) within subclade F1 (Fig. 2A). Clade E, the Clypeariae clade had two main lineages and several smaller supported subclades within them. Clade F, the Archidendron s.s. clade is segregated into three well supported subclades: the lucyi subclade (F1, PP 1.0) that includes three fully supported lineages; the grandiflorum subclade (F2, PP 1.0) that is poorly resolved; and the vaillantii subclade (F3, PP 1.0) that comprises two well supported lineages (PP 0.99; Fig. 2A–C).

Of the 12 species of Archidendron that included more than one accession, seven are monophyletic (A. glabrum (K. Schum.) K. Schum. & Lauterb., A. kanisii R.S. Cowan, A. lucyi F. Muell., A. muellerianum, A. ramiflorum (F. Muell.) Kosterm., A. vaillantii (F. Muell.) F. Muell. and A. whitei), one is unresolved (A. lovelliae (F.M. Bailey) I.C. Nielsen), and four are not monophyletic (A. clypearia (Jack) I.C. Nielsen, A. grandiflorum (Sol. ex. Benth.) I.C. Nielsen, A. hendersonii (F. Muell.) I.C. Nielsen and A. hirsutum I.C. Nielsen). Three of the four samples of A. clypearia form a clade (within clade E, Fig. 2; PP 1.0) with A. borneense (Benth.) I.C. Nielsen nested among them. One sample of A. hendersonii (JA45) is related to A. grandiflorum within clade F2; all other samples of A. hendersonii (Z114, JA103, JA44) form a clade within F3 (PP 1.0; Fig. 2A). Another species falling in both subclades F2 and F3 is A. hirsutum, with one sample (JA46) related to A. forbesii Baker f. and A. lovelliae in subclade F2 (PP 0.99), and the other two (Z113 and JA86) forming a sister pair in subclade F3 (PP 1.0; Fig. 2A).

The consensus network of the final 101-sampled BI trees shows the degree of topological uncertainty between the genera in the Archidendron clade (Fig. 2C). While each respective genus is well-supported as monophyletic (except Archidendropsis and Archidendron as described above) the relationships between the genera are highly uncertain, reflecting the lack of support in the consensus phylogenies. However, the network reinforces the distinction between the two clades of Archidendropsis, and the distinction of the Clyperiae clade from the rest of Archidendron.

The phylogeny of the three cpDNA loci combined lacks support for nearly all nodes (Suppl. material 4: cpDNA tree). Of the supported nodes there are two that are incongruent with the ncDNA tree (Fig. 2): Paraserianthes is sister to Falcataria (UFBS 100), and A. harmsii Malm is supported in the grandiflorum subclade (UFBS 95) sister to A. grandiflorum JA100 (UFBS 97; Suppl. material 4: cpDNA tree). The consensus network of the UFBS replicates (with splits present in at least 20% of trees) reflects the patterns in the ncDNA phylogeny, with four distinct groupings within Archidendron (Fig. 3). Within these groupings, several individuals are placed in different clades to the ncDNA tree: A. hendersonii JA45 is placed in the vaillantii subclade rather than the grandiflorum subclade, and A. harmsii JA74 is in the grandiflorum subclade rather than the lucyi subclade (Fig. 3).

Figure 3. 

Combined cpDNA consensus network of clades within the genus Archidendron. The branches are labelled, and colour coded according to clades in Fig. 2A. Samples that have changed position relative to the ncDNA tree (as discussed in the text) are labelled with their name on the network.

Pollen morphology of Archidendropsis subg. Basaltica

The pollen measurement results are consistent with Nielsen et al. (1983a, 1983b). The pollen of the two species examined (A. basaltica and A. xanthoxylon) are aggregated into symmetrical 16-celled polyads with a diameter of 55–62 μm for A. basaltica and 62–68 μm for A. xanthoxylon (Fig. 4). Fossules were present on the surface of all grains of both species, but they were fainter on the peripheral cells compared to the central ones and overall fainter on A. basaltica compared to A. xanthoxylon (Fig. 4).

Figure 4. 

Scanning electron micrographs of Archidendropsis subg. Basaltica pollen. Archidendropsis xanthoxylon (A BRI AQ0199126 and B BRI AQ0874091) and Archidendropsis basaltica (C BRI AQ0199029 and D BRI AQ01003764).

Discussion

Phylogeny of the Archidendron clade

Our study presents the most taxon-rich sampling of the Archidendron clade of any phylogenetic analyses to date. We confirm that the Archidendron clade sensu Koenen et al. (2020) of Indomalayan-Australasian genera (Acacia, Archidendron, Archidendropsis, Falcataria, Serianthes, Pararchidendron, Paraserianthes and Wallaceodendron) is robustly supported, yet the relationships between the constituent clades are poorly resolved and lack support. This result is not unexpected given we used only four ncDNA loci and that phylogenomic studies based on hundreds of loci also yield short branches with low support across the backbone of the Archidendron clade (Koenen et al. 2020; Demeulenaere et al. 2022; Ringelberg et al. 2022). It has been suggested that this lack of resolution may be the result of extremely rapid speciation and that the backbone of this clade could be best regarded as a polytomy within the Ingoid legumes (Koenen et al. 2020). The differences in published topologies of the Archidendron clade are illustrated in Demeulenaere et al. (2022) but it is clear that further work based on increased sampling of phylogenomic data is required to uncover the evolutionary history of the clade.

Despite the poorly resolved backbone of the Archidendron clade, many clades within it are robustly supported and corroborate published phylogenies, as well as shedding new light on the genera Archidendron and Archidendropsis (Fig. 2). Four genera of the Archidendron clade are confirmed to be monophyletic – Acacia (Miller and Bayer 2001; Luckow et al. 2003; Miller et al. 2003; Brown et al. 2008), Falcataria (Brown et al. 2011), Pararchidendron and Serianthes (Demeulenaere et al. 2022) – and the previously suggested non-monophyly of Archidendron and Archidendropsis (Brown et al. 2008, 2011; Iganci et al. 2016; Demeulenaere et al. 2022; Ringelberg et al. 2022) is confirmed and clarified by increased sampling within these genera.

Phylogenetic relationships within Archidendron

The genus Archidendron is not monophyletic, and the eight series, while useful for identification purposes, do not coincide with evolutionary lineages (Fig. 2). The only series confirmed to be monophyletic was series Ptenopae from the island of New Guinea, the smallest series comprising just two species with two-winged leaf rachises and pinnae: A. ptenopum Verdc. and A. hispidum (Mohlenbr.) Verdc. (Nielsen et al. 1984b). The monophyly of series Calycinae and Pendulosae was not tested, as only one species of each was sampled, however, all other series (Archidendron, Bellae, Clypeariae, Morolobiae, and Stipulatae) are not monophyletic. Archidendron is instead resolved into two well supported lineages, one of which is primarily distributed in western Malesia and mainland Asia (the Clypeariae clade; clade E, Figs 13) and the other (the Archidendron s.s. clade; clade F, Figs 13) mostly restricted to eastern Malesia and Australia. These two lineages have been identified in previous phylogenetic studies but the sampling for each was extremely limited, with at most seven species of one lineage included (Brown et al. 2008, 2011; Iganci et al. 2016; Demeulenaere et al. 2022; Ringelberg et al. 2022). The further segregation of the Archidendron s.s. clade into three well supported lineages, the lucyi (F1), the grandiflorum (F2), and the vaillantii subclades (F3; Figs 23), is novel.

These three subclades of the Archidendron s.s. clade reflect geographic distributions to some extent, but no macromorphological characters have been identified to clearly delineate them. The grandiflorum and vaillantii subclades are predominantly Australian with some southern New Guinean species included, while the lucyi subclade is geographically more broadly distributed in the Lesser Sunda Islands, the Moluccas, through New Guinea to the Solomon Islands with only one species, A. lucyi, extending into northern Australia. Morphologically, the lucyi subclade includes all the sampled species lacking stipules that are not from ser. Clypeariae (i.e. A. calliandrum de Wit, A. harmsii, and A. glabrum), although stipules are reported for other species in this clade, three with stipular glands (A. lucyi, A. megaphyllum Merr. & L.M. Perry, Archidendron sp. nov. JA85), two with stipules only (A. ptenopum and A. hispidum) and A. parviflorum Pulle having both stipular glands and stipules (AAU Balgooy 6769; Nielsen et al. 1984b). All sampled species in the grandiflorum and vaillantii subclades have stipules, except A. arborescens (Kosterm.) I.C. Nielsen and A. forbesii, which have stipular glands (BM000946689; BRI AQ0380081; BRI AQ052589; Nielsen et al. 1984b) The placement of an undescribed species (Archidendron sp. nov. JA85) from the Aru Islands (Moluccas) in the lucyi subclade fits the geographic range. Ivan Nielsen noted this as a putative new species in October 1998 (AAU Balgooy 6769) but it does not align with any of the 20 imperfectly known species he outlined (Nielsen et al. 1984b), highlighting that further taxonomic work is required.

Three species in the Archidendron s.s. clade were not resolved as monophyletic (Fig. 2A), although it is unlikely these are issues with species delimitation. The paraphyly of A. grandiflorum (Fig. 2), a morphologically consistent species across a large geographic range (Brown pers. obs.), could be the result of potentially rapid and recent divergence or may be due to insufficient phylogenetically informative characters in this study. The latter could also apply to the polyphyletic species (A. hendersonii and A hirsutum), as A. hendersonii JA45, which is placed separately from the other conspecific samples is missing data for two of the four ncDNA loci (Table 1). However, this was not the case for A. hirsutum JA46. Re-examination of the vouchers of all accessions of A. hendersonii and A. hirsutum confirmed their identifications, suggesting that incomplete lineage sorting or paralogy problems associated with one or more nuclear loci could explain these non-monophyletic species; further data are required to investigate this.

The Clypeariae clade (clade E, Figs 23) includes all sampled species of ser. Clypeariae (19/51), except one accession of A. clypearia (JA95) from Papua New Guinea and A. pellitum (Gagnep.) I.C. Nielsen from Vietnam. Series Clypeariae was previously recognised in Pithecellobium as section Clypearia until Nielsen et al. (1984b) expanded Archidendron based on evidence from shared wood anatomy, inflorescence and pod morphology (Nielsen et al. 1984b). Characters of the pods are also useful to differentiate series Clypeariae from the rest of Archidendron. Nielsen et al. (1984b) described six pod types and most species of ser. Clypeariae have pod type 2 (long funicle, opens ventral suture first) or 6 (straight pods with overgrown seeds), while the other series primarily have pod type 1 (opens dorsal suture first, short funicles). Seeds of ser. Clypeariae are usually flattened and are not embedded in the pericarp, which is possibly linked to characteristics of the pod, such as dryness (de Wit 1942; Nielsen 1981, 1992; Nielsen et al. 1984b). Additionally, the combination of lack of stipules and solitary, stipitate ovaries delineates ser. Clypeariae (Nielsen et al. 1984b). Individually though, these characters are not diagnostic, as some species with sessile ovaries are placed in ser. Clypeariae (e.g. A. occultatum (Gagnep.) I.C. Nielsen and A. turgidum (Merr.) I.C. Nielsen), other species lacking stipules are placed in series Archidendron (e.g. A. harmsii and A. tjendana (Kosterm.) I.C. Nielsen), and two Philippine species of ser. Clypeariae (A. apoense (Elmer) I.C. Nielsen and A. merrillii (J.F. Macbr.) I.C. Nielsen) have more than one ovary but both are stipitate (Nielsen et al. 1984b). Given these morphological differences of ser. Clypeariae from the rest of Archidendron, together with the non-monophyly of the genus, there are grounds for segregating Clypeariae as a distinct genus; however, we are not proposing such a taxonomic change here for several reasons. First, there are many shared morphological characters between species of Archidendron s.l.; second, the shallow backbone of the ncDNA tree remains poorly supported with topological uncertainty between lineages; third, the placement of two species of ser. Clypeariae within the Archidendron s.s. clade (clade F; A. clypearia var. velutinum (Merr. & L.M. Perry) I.C. Nielsen and A. pellitum) raises further doubts; and fourth, phylogenetic sampling of species remains incomplete. All these issues suggest that denser taxon sampling and larger phylogenomic datasets are required before re-classifying Archidendron as two genera.

Archidendron clypearia is the most widespread species of Archidendron, found from India through to Papua New Guinea. The morphological variation within A. clypearia has been used to recognise four infraspecific taxa (Legume Phylogeny Working Group 2021): subsp. clypearia, subsp. subcoriaceum (Thwaites) M.G. Gangop & Chakrab., var. sessiliflorum (Merr.) I.C. Nielsen, and var. velutinum. The one accession of A. clypearia placed outside the Clypeariae clade (JA95) (Fig. 2A) has been identified as var. velutinum (Brown, pers. obs. of CANB525617; previously only identified to species level by the collector), the only infraspecific taxon found in eastern Malesia (Sulawesi, Moluccas and PNG). The three other samples of A. clypearia included in the phylogeny have not been assigned to infraspecific taxa but they are not likely var. velutinum, as they are from Malaysia and Vietnam and lack the woolly to velutinous hairs on the lower surface of the leaflets (Brown per. obs.). Taxonomic revision and denser phylogenetic sampling of A. clypearia from across its morphological and geographic range is required to verify this placement, delineate the taxa and investigate if var. velutinum should be raised to species level (Merrill and Perry 1942) or if there are intermediate forms as suggested by Kostermans (1966). The only other species of series Clypeariae that extends into eastern Malesia, A. palauense (Kaneh.) I.C. Nielsen, from the Moluccas through to the Solomon Islands (Nielsen et al. 1984b), was not sampled here. There are no obvious morphological characters that support placement of A. pellitum outside the Clypeariae clade, as it has the full combination of diagnostic characters of ser. Clypeariae: compressed pods with a long (3–5 mm) funicle, stipitate single ovary and no visible stipules (US 2515891; P01818442; Nielsen 1981). In addition, no evidence of paralogy in the nuclear loci of A. pellitum and A. clypearia var. velutinum (JA95) was noted in this study; all sequences suggest they fall in the A. lucyi subclade.

The last revision of the genus Archidendron (Nielsen et al. 1984b) significantly advanced our understanding of the genus but more detailed taxonomic study is still required, focusing especially on the large number of species known from incomplete material and widespread morphologically variable species, such as A. clypearia. To resolve the backbone of the Archidendron clade and inform decisions about generic delimitation to deal with the non-monophyly of Archidendron, we recommend further sampling of ser. Clypearia, particularly from the Wallacean region of Malesia (i.e. Moluccas, Sulawesi, Philippines), together with further genomic sampling.

Phylogenetic relationships within Archidendropsis

While Archidendropsis is not monophyletic, its two subgenera (Archidendropsis and Basaltica) are (Fig. 2). The species within each subgenus have long been recognised as closely related (Bentham 1875; Nielsen 1981) but the two subgenera themselves have not always been associated with each other. For example, Bentham (1875) placed the species of each subgenus in different sections of Albizia based on inflorescence shape. Species of subgenus Archidendropsis that have flowers arranged in cylindrical spikes were placed by Bentham (1875) in Albizia section Lophantha Benth. (an illegitimate name later corrected to Albizia section Pachysperma (Benth.) Fosberg by Fosberg (1965)). Within this section they were separated from the other taxa, which are now recognised as Paraserianthes, into series Platyspermae Benth. because they have flattened, broadly orbiculate seeds (Bentham 1875). The two species of subgenus Basaltica known at that time (A. basaltica and A. thozetiana (F. Muell.) I.C. Nielsen) were placed by Bentham in his large section Eualbizzia distinguished by flowers in globular heads and flattened orbicular seeds (Bentham 1875). Within that section, these taxa were placed into series Obtusifolia, which corresponds to the Australian species with 1–2 jugate leaves, ovate, oblong or obtuse leaflets, short petioles, pedunculate heads in the axils, and small sessile flowers.

It was only recently that the species of the two subgenera were united within Archidendropsis by Nielsen (1983) based on characters of the fruit and seed: pods dehiscent along both sutures, and seeds that are winged, thin-walled and lack a pleurogram. However, Nielsen himself questioned whether the subgenera should be congeneric, noting that if they were not, “the evolution of the winged thin walled seeds without pleurogram should have happened twice” (Nielsen et al. 1983a: p. 337). The results presented here (Fig. 2) alongside two recent phylogenomic analyses (Demeulenaere et al. 2022; Ringelberg et al. 2022) show that the two subgenera of Archidendropsis do not form a monophyletic group, suggesting these seed characteristics are indeed the result of convergent evolution.

The presence of a pleurogram is common in mimosoid genera (Gunn 1984), and is considered to have evolved multiple times (Maumont 1993). Within the Archidendron clade, Archidendron and Archidendropsis are the only two genera whose seeds lack a pleurogram (Nielsen 1992). The absence of a pleurogram has been associated with short-lived ‘recalcitrant’ seeds (i.e. seeds which lack dormancy and can be viviparous; Nielsen 1992) and has been thought to be an adaptive response to humid environments (Corner 1951 in Nielsen 1992; Maumont 1993). Like the absence of a pleurogram, winged seeds are also rare in mimosoids occurring in only eight genera, including Archidendropsis (Gunn 1984). The possession of a winged seed has been suggested to be an adaptation for wind-dispersal but there have been no published observations of this in Archidendropsis (Gunn 1984; Nielsen 1992). The short viability of Archidendropsis seeds has been linked to the restricted geographic ranges of individual species (Nielsen 1983). However, humidity may be a more important determinant of these distributions, as the ranges of the two Australian species occurring in drier, non-rainforest habitats are more than 10 times larger than the rainforest species (e.g. A. basaltica ≥ 750,000 km2 compared to A. xanthoxylon c. 8,750 km2 (AVH 2021)). The habitats of A. basaltica and A. thozetiana are also more open than for A. xanthoxylon, but these two species generally have narrower wings on their seeds than the rainforest species A. xanthoxylon (Cowan 1998), suggesting that the wing is unlikely to have an impact on wind dispersal. Morphological features that have been used to unite the two subgenera in Archidendropsis are thus homoplasious and not useful for generic delimitation.

The non-monophyly and clear morphological distinctions between them means that the two subgenera can no longer be treated as congeneric and need to be placed in separate genera. As the type of Archidendropsis (A. fulgens (Labill.) I.C. Nielsen) is from subg. Archidendropsis, it is subg. Basaltica that requires a new name. No name exists at the generic level for these taxa, as they have previously been placed in Acacia, Albizia and Archidendropsis (Mueller 1859; Bentham 1875; Fosberg 1965; Nielsen 1983), names which are all typified by other taxa.

In addition to the aforementioned morphological differences between the two subgenera, species of subg. Basaltica are endemic to Australia, whereas those of subg. Archidendropsis are found in New Caledonia, New Britain, the Solomon Islands and on the island of New Guinea (Fig. 1B). Furthermore, there are several pollen characters separating the two subgenera (Nielsen et al. 1983a). Pollen of subg. Basaltica has isometric channels in the tectum and is aggregated into smaller polyads (55–68 μm), cf (80–120 μm) for subg. Archidendropsis where the tectum has non-isometric channels (Fig. 4; Nielsen et al. 1983a). The pollen surface of subg. Basaltica has fossules on the central cells, with either faint fossules or smooth peripheral cells, while in subg. Archidendropsis the surface of all pollen cells has small rounded areoles or deep fossules (Fig. 4; Nielsen et al. 1983a). Species of subg. Basaltica have sessile flowers arranged in globular pedunculate heads, rather than in spikes or racemes. Although one species of subg. Archidendropsis, A. fournieri (Vieill.) I.C. Nielsen, also has flowers arranged in globular pedunculate heads, it does not share the other diagnostic characters of subg. Basaltica, it is endemic to New Caledonia, its seeds are not winged, and the diameter of the pollen polyads is larger, fitting within the size range for subg. Archidendropsis (Nielsen 1983). Another character noted by Nielsen et al. (1983a) to differentiate the two subgenera, was the shape of the stipules, with those of subg. Basaltica being small and often developed into stipular spines (to 1.2 mm long; Brown pers. obs.; Fig. 5F) that are early caducous. However, the stipules of A. xanthoxylon were not recorded by Nielsen et al. (1983a) and are not like other Australian species being 1.2–3 mm long, ovate to triangular, dark gland-like and persistent (Brown, pers. obs., BRI AQ022813, BRI AQ0234095, BRI AQ0771148, BRI AQ199127, BRI AQ0199128; Fig. 5G). These stipules do differ, however, from those of the species of subg. Archidendropsis which, if present, are usually small (c. 1 mm), ovate or filiform and often caducous (Nielsen 1983).

Figure 5. 

Morphology of Heliodendron. Plate showing diagnostic features of the new genus Heliodendron A inflorescence of H. thozetianum, Hazelwood Gorge, west of Mackay, Queensland (photo, Stuart Worboys, Australian Tropical Herbarium) B single flower of H. basalticum (BRI AQ0648454) showing hairs on calyx and corolla C mature bud of H. xanthoxylon (BRI AQ0874091) showing hairs on the lobes of the calyx and corolla D seeds of H. basalticum (BRI AQ0746724) E overall pod shape of H. xanthoxylon (BRI AQ0234095) F small rigid stipules of H. basalticum (BRI AQ0673898) G glandular stipule of H. xanthoxylon (BRI AQ0771148). Whole leaf showing overall leaflet size and shape of H H. basalticum (BRI AQ0648454) I H. thozetianum (BRI AQ0611464), and J H. xanthoxylon (BRI AQ0874091). Habit of H. basalticum from K Bladensberg National Park, Queensland (photo, Dale Richter, Queensland Herbarium) L 65 km west south-west of Blackall, Queensland (photo, Murray Fagg, Australian Plant Image Index, Australian National Botanic Gardens).

Flowers arranged in globular heads, seeds lacking a pleurogram with a narrow peripheral membranous wing and flat, narrowly oblong, brown pods opening along both sutures distinguish this new genus from other Australian mimosoid legumes, and the keys in Flora of Australia (Cowan 1998) and available on KeyBase (Bean 2021; KeyBase 2021) still remain suitable.

Taxonomic treatment

Heliodendron Gill.K. Br. & Bayly, gen. nov.

Fig. 5

Diagnosis

A genus of mimosoid legumes similar to Archidendropsis but differing in the following combination of features: inflorescences of glomerules, calyx and corolla with hairs (restricted to the lobes in H. xanthoxylon); stipules either small (to 1.2 mm) rigid and caducous or glandular (1.2–3 mm long) and persistent; pollen arranged in polyads diameter of 55–68 μm; pollen tectum with isometric channels. In contrast, Archidendropsis has inflorescences of spikes, spiciform racemes, racemes or in one species glomerules, but when in glomerules the calyx and corolla are glabrous; stipules (if present) either small (c. 1mm) ovate or filiform and often caducous, or large auriculate, orbicular, or cordate and persistent; pollen polyad diameter of 80–120 μm, pollen tectum with non-isometric channels.

Description

Trees or shrubs, with terete branchlets. Stipules either resembling small thorns to 1.2 mm long that are early caducous, or persistent circular-ovate glands 1–3 mm in diameter. Leaves bipinnate, pinnae 1–2 pairs with 1.5–11 leaflet pairs per pinna; glands at the junction of pinnae circular or triangular to rhombic, +/- circular glands at the junction of leaflet petiolules. Leaflets opposite, subsessile (0.2–0.7 mm) or long (3.5–7 mm) petiolulate; elliptic to elliptic-lanceolate or oblong, 2–38 mm × 1.5–15 mm, glabrous to puberulous. Inflorescence of globular heads 0.5–1.7 mm in diameter, either simple or arranged into a panicle up to 35 cm long. Flowers: homomorphic, yellow to cream, sessile. Calyx 1.5–3 mm long, tubular to subcampanulate; corolla 2.5–7 mm long, tubular to narrowly campanulate. Ovary 0.8–2 mm long, solitary and shortly stipitate; stamens numerous 5–9 mm long, united basally into a tube that equals or slightly exceeds the corolla tube. Pollen 16-celled polyads with a diameter of 55–68 μm, tectum with isometric channels. Pod brown, valves chartaceous, 6–22 cm × 0.5–2.5 mm, oblong, flat and dehiscing along both sutures. Seeds lacking a pleurogram, flat, circular to ovate or obliquely ovate, 5–13 mm, with a narrow 0.2–1 mm peripheral, membranous wing. Fig. 5.

Type

Heliodendron basalticum (F. Muell.) Gill.K. Br. & Bayly ≡ Acacia basaltica F. Muell., Journal of the Proceedings of the Linnean Society, Botany 3: 146 (1859)

Etymology

From the Greek helios (sun) and dendron (tree) alluding to the endemic distribution of the genus in the Australian state of Queensland, widely known as the “sunshine state”, the globular, sun-like inflorescences of yellow flowers, and the tree habit (Fig. 5A, K, L) and also in reference to the genera Archidendropsis (in which the species were previous placed) and Archidendron (which they resemble).

Homotypic synonym

Archidendropsis subg. Basaltica I.C. Nielsen, Bulletin du Muséum National d’Histoire Naturelle. Section B, Adansonia: Botanique Phytochimie 5(3): 325 (1983).

Notes

We have chosen to create a new name for this genus rather than making a new combination based on the name Archidendropsis subg. Basaltica. This is because using the name “Basaltica” at generic rank would require a change of epithet for the most widespread species in the genus under Art. 23.4 of the International Code of Nomenclature for algae, fungi, and plants (Turland et al. 2018). To minimise taxonomic change, and to avoid potential confusion, we would rather that the species retains its well-known epithet, which has been in continuous use since 1859.

The genus includes the following three species, all endemic to Queensland, Australia (Fig. 1B).

Heliodendron basalticum (F. Muell.) Gill.K. Br. & Bayly, comb. nov.

Basionym

Acacia basaltica F. Muell., Journal of the Proceedings of the Linnean Society, Botany 3: 146 (1859). ≡ Albizia basaltica (F. Muell.) Benth., Flora Australiensis 2: 422 (1864); Archidendropsis basaltica (F. Muell.) I.C. Nielsen, Bulletin du Muséum National d’Histoire Naturelle. Section B, Adansonia: Botanique Phytochimie 5(3): 326 (1983).

Type

Peak Downs, F. Mueller 42 (holotype: MEL 594732A image!; isotype K000822321 image!).

Heliodendron thozetianum (F. Muell.) Gill.K. Br. & Bayly, comb. nov.

Basionym

Acacia thozetiana F. Muell., Fragmenta Phytographiae Australiae 4(24): 9 (1863). ≡ Albizia thozetiana (F. Muell.) F. Muell. ex Benth., Flora Australiensis 2: 422 (1864); Archidendropsis thozetiana (F. Muell.) I.C. Nielsen, Bulletin du Muséum National d’Histoire Naturelle. Section B, Adansonia: Botanique Phytochimie 5(3): 326 (1983).

Type

Fort Cooper, [A. Thozet?] no. 29. (Lectotype, designated by R.S. Cowan, Nuytsia 11: 13 (1996)): MEL 595338A image!; residual syntypes: MEL 595339A, MEL 595340A, MEL 595342A, MEL 595377A].

Heliodendron xanthoxylon (C.T. White & W.D. Francis) Gill.K. Br. & Bayly, comb. nov.

Basionym

Albizia xanthoxylon C.T. White & W.D. Francis, Proceedings of the Royal Society of Queensland 41: 141, t. X (1929). Archidendropsis xanthoxylon (C.T. White & W.D. Francis) I.C. Nielsen, Bulletin du Muséum National d’Histoire Naturelle. Section B, Adansonia: Botanique Phytochimie 5(3): 326 (1983).

Type

Atherton District, North Queensland, Overseer brothers s.n. (Provisional Forestry Board), end of October, 1927 (Lectotype, designated by I.C. Nielsen as “Type”, Bulletin du Muséum National d’Histoire Naturelle. Section B, Adansonia: Botanique Phytochimie 5(3): 341 (1983): BRI AQ022813! [2 sheets]; isolectotypes: DNA D0053218 image!, K000822329 image!, MEL 1562403A image!).

Notes

The protologue of Albizia xanthoxylon (White and Francis 1929) gave a location, collector name and month of the collection but did not indicate the herbarium in which the type was held, thus meaning that all specimens of this gathering could be considered syntypes. However, it appears that Nielsen inadvertently typified this taxon, according to Art. 7.11 of the ICN (Turland et al. 2018), when providing the description for the new combination of Archidendropsis xanthoxylon with the text “Type: Overseer Brothers, Australia, N. Queensland, Atherton District, Oct 1927, fl. fr. (holo-,BRI; iso-K)” (Nielsen et al. 1983a: p. 341). We believe this satisfies the requirements of Art. 7.11 to effectively lectotypify the name, which means that the BRI specimen is the lectotype and the K specimen is the isolectotype. Interestingly, the material illustrated in the protologue is clearly the isolectotype at K, as it is the only type specimen of Heliodendron xanthoxylon with pods, and the structure of the inflorescence and leaves is almost identical (K000822329; White and Francis 1929).

In Flora of Australia, Cowan (1998) cited BRI as holding an isotype as well as the holotype of this taxon; however, the two sheets have the same collection details, are labelled as sheet 1 of 2 and sheet 2 of 2, and share a single accession number (BRI AQ022813). Therefore, it is herein determined that these are the one collection, and both represent the holotype (now lectotype; BRI AQ022813).

Conclusion

We present the most densely sampled phylogeny of the genera Archidendron and Archidendropsis to date and confirm that both genera are not monophyletic. The well supported clades within the Archidendron clade based on four nuclear markers agree with more data-rich phylogenomic data sets now being generated. A new genus, Heliodendron, endemic to Queensland (Australia), is described for the Australian members of the former Archidendropsis subg. Basaltica. Further sampling of species from subg. Archidendropsis would be beneficial, particularly to ascertain the relationships of the globular flowered A. fournieri and the non-New Caledonian representatives of Archidendropsis s.s. While Archidendron is also not monophyletic, no nomenclatural changes are made, because low phylogenetic support and high topological uncertainty between genera of the Archidendron clade mean that the relationships between the two clades of Archidendron remain uncertain. In addition, discrete macromorphological characters need to be identified to distinguish the two lineages of Archidendron as the basis for generic re-delimitation. A taxonomic revision of the widespread polymorphic A. clypearia would aid this, as our results indicate var. velutinum from eastern Malesia may represent a distinct species. Phylogenomic data and additional sampling of this species would be beneficial before taxonomic changes are made.

Acknowledgements

This research was funded by an Australia and Pacific Science Foundation grant (APSF14-4: Systematics and evolution of Archidendron, the largest group of tropical legumes in the Austral region) and an Australia Awards Scholarship to Javier Aju to undertake his Masters. We thank the following herbaria for providing access to specimens, including destructive sampling: AAU, BISH, BRI, CANB, CNS, KEP, KUN, L, NY, MEL and MELU. We thank Shelly James (then BISH now PERTH), Stuart Worboys (CNS) and George Weiblen (Bell Museum) for providing material, and Jo Palmer and Kirsten Cowley (CANB) who sampled and imaged specimens for us. Field work for this project was conducted in Queensland under the permit WITK15692815, issued by the Department of Environment and Heritage Protection, Queensland Government. Darren Crayn is thanked for his support and guidance in the fieldwork to collect samples of Archidendron in north Queensland. Melodina Fabillo is appreciatively recognised for her work on the pollen morphology of Heliodendron, generating Figure 5, and providing feedback on the draft manuscript. Jens Ringelberg is thanked for generating the maps of Archidendron and Archidendropsis s.l. in Figure 1. We also thank Tony Bean, David Halford and Peter Bostock for nomenclatural discussions. Thank you to Else Demeulenaere and Erik Koenen for providing helpful comments and suggestions during the review process to improve the manuscript. Lastly, we thank Colin Hughes for inviting us to be involved in this special issue of Advances in Legume Systematics.

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Supplementary materials

Supplementary material 1 

Primer sequences and PCR variations

Gillian K. Brown, Javier Aju, Michael J. Bayly, Daniel J. Murphy, Todd G.B. McLay

Data type: Pdf file.

Explanation note: The reference for the primer and their PCR conditions are provided, along with the variations for PCR reagents and cycling conditions for the initial PCR in the two-step PCR process. * only used for sanger sequencing so no variations to note. Standard PCR reagents prior to variation consisted of 2X QIAGEN PCR buffer (QIAGEN), 5 mM of each dNTP (Bioline), 1 µl of each primer (10 µM), 1.25 µl of dimethyl sulfoxide (DMSO, 99.5%; Sigma-Aldrich), 1 U of Taq DNA polymerase, 100 ng of template and made up to 25 µl with ultra pure water per reaction. Reagent variations, A: not varied; B: 200 ng DNA, 1.2 µl BSA instead of DMSO; C: 200 ng DNA; D: 200ng DNA, 6 μM each primer, 1.5 µl MgCl2, 0.9 µl DMSO and 0.1 µl Taq; E: 6 µM each primer. Cycle variations: Z: 94 °C for 15 mins; 30 cycles of 94 °C for 20 sec, 61 °C for 20 sec, 72 °C for 2 mins; 72 °C for 5 mins; Y: 94 °C for 15 mins; 35 cycles of 94 °C for 20 sec, 61 °C for 20 sec, 72 °C for 2 mins; 72 °C for 5 mins; X: 94 °C for 15 mins; 35 cycles of 94 °C for 20 sec, 55 °C for 30 sec, 72 °C for 2 mins; 72 °C for 7 mins; W: 94 °C for 15 mins; 40 cycles of 94 °C for 20 sec, 50 °C for 1 min, 72 °C for 3 mins; 72 °C for 7 mins; V: 80 °C for 5 mins; 40 cycles of 95 °C for 1 min, 50 °C for 1 min with 0.3 °C/sec ramp, 65 °C for 4 mins; 65 °C for 5 mins; U: 94 °C for 5 mins; 30 cycles of 94 °C for 30 sec, 53 °C for 30 sec, 72 °C for 1 min; 72 °C for 7 mins; T: 80 °C for 5 mins; 30 cycles of 95 °C for 1 min, 50 °C for wwith 0.3 °C/sec ramp, 65 °C for 4 mins; 65 °C for 5 mins.

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Download file (643.96 kb)
Supplementary material 2 

SHMT network and tree

Gillian K. Brown, Javier Aju, Michael J. Bayly, Daniel J. Murphy, Todd G.B. McLay

Data type: Pdf file.

Explanation note: Neighbour-joining tree and NeighbourNet network are presented with individual samples with more than one allele coloured to highlight their positions. The samples are coloured the same in both the tree and network. The clades that are congruent with Fig. 2 (B, C, D, D1, D2, F1, F2) are labelled. The sequences from species of Albizia (Z106, JA137) were removed as they occur on a very long branch relative to the rest of the samples in the network.

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Download file (376.69 kb)
Supplementary material 3 

RBPCO network and tree

Gillian K. Brown, Javier Aju, Michael J. Bayly, Daniel J. Murphy, Todd G.B. McLay

Data type: Pdf file.

Explanation note: Neighbour-joining tree and NeighbourNet network are presented with individual samples with more than one allele coloured to highlight their positions. The samples are coloured are the same in both the tree and network. Clade B, which is congruent with Fig. 2 is labelled.

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Download file (30.54 kb)
Supplementary material 4 

cpDNA tree

Gillian K. Brown, Javier Aju, Michael J. Bayly, Daniel J. Murphy, Todd G.B. McLay

Data type: Pdf file.

Explanation note: IQ-Tree of combined cpDNA loci, with all UFBS values shown. The two clades that are congruent with of Fig. 2 are labelled (A and F). Arrows indicate the placement of the two supported incongruences mentioned in the results text.

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Download file (34.82 kb)
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