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Research Article
Hedyotis konhanungensis (Rubiaceae): A new species from the central highlands of Vietnam
expand article infoBui Hong Quang‡§, Khang Sinh Nguyen‡§, Tuan Anh Le|, Le Thi Mai Linh‡, Quoc Luan Nguyen, Duy Hoang Vu Ngo, Lei Wu#, Suman Neupane¤
‡ Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, Hanoi, Vietnam
§ Graduate University of Science and Technology, Hanoi, Vietnam
| Mien Trung Institute for Scientific Research, Vietnam National Museum of Nature, Thua Thien Hue, Vietnam
¶ Kon Ka Kinh National Park, Gia Lai, Vietnam
# Central South University of Forestry and Technology, Changsha, China
¤ Murray State University, Murray, United States of America

Corresponding author: Suman Neupane ( sneupane2@murraystate.edu )

Academic editor: Yasen Mutafchiev
© 2023 Bui Hong Quang, Khang Sinh Nguyen, Tuan Anh Le, Le Thi Mai Linh, Quoc Luan Nguyen, Duy Hoang Vu Ngo, Lei Wu, Suman Neupane.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Quang BH, Nguyen KS, Le TA, Linh LTM, Nguyen QL, Ngo DHV, Wu L, Neupane S (2023) Hedyotis konhanungensis (Rubiaceae): A new species from the central highlands of Vietnam. PhytoKeys 221: 73-84. https://doi.org/10.3897/phytokeys.221.95895
Open Access

Abstract

A new species of Hedyotis L. (Rubiaceae), Hedyotis konhanungensis B.H. Quang, T.A. Le, K.S. Nguyen & Neupane, is described and illustrated from the central highlands of Vietnam based on morphological and phylogenetic evidence. The new species belongs to the morphologically diverse tribe Spermacoceae (ca. 1000 species) of the family Rubiaceae, which is represented by 70–80 species in Vietnam. The phylogenetic analysis, based on four DNA regions (ITS, ETS, petD, rps 16), confirms the new species’ placement within the genus Hedyotis – one of the largest genera in the tribe, comprising ca. 180 species across Asia and the Pacific. Hedyotis konhanungensis is morphologically distinct from all southeastern Asian Hedyotis L. in its set of traits such as leaf type (shape and thickness), growth habit, and floral parts (color of inflorescence axis and the shape of calyx lobes). The new species shows similarities with Hedyotis shenzhenensis, H. shiuyingiae, and H. yangchunensis from China in its herbaceous habit, fleshy ovate leaf blades, and dark purple floral parts, but it is phylogenetically distinct and can be distinguished from them by the following combination of morphological traits: habit with slightly smaller stature (<25 cm), broadly ovate or deltoid stipules with cuspidate apex and entire margin, and ovate or nearly ovate calyx lobes.

Keywords

Gia Lai Province, Hedyotis-Oldenlandia complex, Indochina, phylogenetics, Spermacoceae, taxonomy

Introduction

The Asian-Pacific genus Hedyotis L. (ca. 180 species) lies within a polymorphic, mainly herbaceous tribe Spermacoceae (ca. 1000 species) of the family Rubiaceae. In Vietnam, this tribe is represented by 70–80 species belonging to the genera Dimetia (Wight & Arn.) Meisn., Debia Neupane & N.Wikstr., Exallage Bremek., Leptopetalum Hook. & Arn., Hedyotis L., Involucrella (Benth. & Hook.f.) Neupane & N.Wikstr., Neanotis W.H.Lewis, Oldenlandia L., and Spermacoce L. (Govaerts et al. 2022). The genus Hedyotis and its related genera that form the Hedyotis-Oldenlandia complex have a long history of taxonomic confusion and disagreement due to the use of inconsistent and overlapping characters in the generic delimitations. The genus Hedyotis is currently treated in a narrow sense based on the molecular phylogenies (Guo et al. 2013; Wikström et al. 2013; Neupane et al. 2015) where members of it are united by their predominantly shrubby to tree-like habit, septicidal capsules, flattened seeds, and tropical upland distributions in Asia and the Pacific. The species of this genus are mostly found in the mid or high-elevation slopes (to 4000 m a.s.l.) of Asia (Sri Lanka, southern India, SE China, Indochina, Malesia), Papuasia, and NW Pacific (Micronesian islands). In Vietnam there are about 20 species reported in the flora of this country (Pitard 1922; Pham 2003; Tran 2005; Do et al. 2013; Govaerts et al. 2022) but the actual number could be as high as 40 species since many species listed under Oldenlandia share the diplophragmous capsule characteristic of Hedyotis (pers. obs.).

During a botanical field survey in Kon Ha Nung Biosphere Reserve (UNESCO 2021) of the highlands of Central Vietnam, we came across a population of Spermacoceae (collection number LTA 531) with the following morphological features: perennial herbs, opposite obovate to nearly oval leaf blades, interpetiolar entire stipules with cuspidate apex, 4-merous flowers, bilobed stigmas, inferior ovary, and many-seeded, diplophragmous capsules with persistent ovate or nearly oval calyx lobes. The morphological features, specifically the presence of diplophragmous capsules, observed in the new population of Spermacoceae align with the diagnostic characteristics of the genus Hedyotis as outlined in Wikström et al. (2013) and Neupane et al. (2015). Following a thorough review of the taxonomic literature on the genus Hedyotis in Vietnam and surrounding regions, including Pitard (1922), Fukuoka (1970), Pham (2003), Tran (2005), Chen and Taylor (2011), Wikström et al. (2013), and Neupane et al. (2015), as well as a comprehensive morphological comparison with closely related species such as Hedyotis shenzhenensis T.Chen, H. shiuyingiae T.Chen, and H. yangchunensis Ko & Zhang, and utilizing phylogenetic analysis to determine its placement within the Spermacoceae, we have determined that our specimens represent a previously undescribed species within the genus Hedyotis. This species is hereby named Hedyotis konhanungensis.

Materials and methods

Morphological study

Our collected specimens were compared with all described species from southeast Asia and southern China by studying relevant literature and examining digital herbarium images. Morphological characters were recorded using Nikon SMZ745/SMZ745T stereoscopic microscope and photographs of vegetative and floral parts were taken both in the field and from the samples preserved in 70% ethanol using Canon EOS 7D. The type specimens have been stored in the following three herbaria (acronyms follow Thiers 2022, continuously updated): Vietnam National Museum of Nature (VNMN), Institute of Ecology and Biological Resources, Vietnam Academy of Sciences and Technology (HN), and Kon Ka Kinh National Park.

Phylogenetic analysis

To establish its phylogenetic position within the tribe Spermacoceae, total genomic DNA was extracted from silica-dried material with the DNeasy Plant Kit (Qiagen, Valencia, California, U.S.A.). Four DNA regions (nuclear genome: ITS, ETS; plastid genome: petD, rps16) that were used in our earlier studies (Neupane et al. 2015, Neupane et al. 2017), were selected for amplification from this sample. Amplifications were performed in a 25 μl reaction mixture composed of 1 μl of each primer (10 μM), 1 μl of DNA template, 12.5 μl of GoTaq Green Master Mix (Promega, Madison, Wisconsin, U.S.A.), 9.5 μl of water. The amplification protocol for nuclear and chloroplast regions follows Kårehed et al. (2008) and Groeninckx et al. (2009) respectively. Amplified PCR products were purified using ExoSAP-IT PCR Product Cleanup (Thermo Fisher Scientific) following the manufacturer’s protocols and sequenced at Apical Scientific Company for sequencing (Selangor, Malaysia).

We added the DNA sequences of our sample to our existing DNA data matrix (Suppl. material 1). The GenBank accession numbers for our sample were OQ401065, OQ401066, OQ458733, and OQ401067, which correspond to the rps16, petD, ITS, and ETS regions, respectively. We also included additional sequences representing the ITS, petD, and rps16 regions for Hedyotis yangchunensis, Hedyotis shenzhenensis, and Hedyotis shiuyingiae, obtained from Guo et al. (2013) and available in GenBank. Each of these DNA regions was aligned using MAFFT v.7 (Katoh and Standley 2013) and concatenated into a single matrix Suppl. material 2) to infer the phylogeny. Phylogenetic analysis was conducted on the combined matrix under the maximum likelihood (ML) framework with four partition schemes (ITS, ETS, petD, rps16) for their own substitution model (GTR+GAMMA) parameters using RAxML v.8.2.12 (Stamatakis 2014). The RAxML tree search and bootstrap analysis (1000 rapid bootstrap replicates for clade support) were conducted on CIPRES (Miller et al. 2010).

Results

Molecular phylogeny

The Maximum likelihood tree obtained from RAxML analysis on the concatenated data confirms the position of our sample from Vietnam within Hedyotis and distinct from H. yangchunensis, H. shenzhenensis, and H. shiuyingiae (Fig. 1, Suppl. material 3) The new species is nested within the clade (BS = 85%) representing Hedyotis from Sri-Lanka, southeast Asia (primarily Borneo), and New Guinea. The new species appears sister to the Sri Lankan clade, however, this phylogenetic position is considered unresolved due to weak bootstrap support (BS = 50%).

Figure 1. 

Maximum likelihood phylogenetic tree of Hedyotis based on the combined nuclear (ITS, ETS) and plastid (petD, rps16) data. The taxa discussed in the paper and the new species are in bold. Values at the nodes represent bootstrap support (BS).

Taxonomic treatment

Hedyotis konhanungensis B.H.Quang, T.A.Le, K.S.Nguyen & Neupane, sp. nov.

urn:lsid:ipni.org:names:77315486-1
Figs 2, 3, Table 1

Type

Vietnam. Central Highlands of Vietnam, Kon Ha Nung Biosphere Reserve, Gia Lai province: K’Bang District, Kon Pne Commune, 14°20'53"N, 108°20'48"E, primary evergreen forest slopes at elevation 1150 m a.s.l., 28 November 2021, Nguyen Quoc Luan, Ngo Duy Hoang Vu & Le Tuan Anh LTA 531 (holotype: VNMN!; isotypes: HN!).

Diagnosis

Hedyotis konhanungensis is similar to H. shenzhenensis, H. shiuyingiae and H. yangchunensis from southeastern China (Guangdong and Hongkong) in the morphology of the leaf blades, floral bracts, dichasial cymes, and fruits, but differs from them by its broadly ovate or deltoid (vs. triangular or broadly triangular) stipules with entire (vs. hairy or lacerated) margins and cuspidate (vs. acute) apex, suborbicular or broadly oval (vs. subovate or ovate to lanceolate) lowest floral bracts, ovate or nearly oval (vs. triangular or subulate to lanceolate) persistent calyx lobes on fruits, and stamens in long-styled flowers inserted in lower ¼ or near the base (vs. at the middle or near the mouth) of the corolla tube (Table 1).

Table 1.
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Morphological comparison of Hedyotis konhanungensis with its putative closest allies. The characters of H. shenzhenensis T.Chen, H. shiuyingiae T.Chen and H. yangchunensis W.C.Ko & Zhang are taken from Chen (2007, 2008), and Gao (1995) and their type specimens respectively.

Morphological characters H. konhanungensis H. shenzhenensis H. shiuyingiae H. yangchunensis
Plant height, including the inflorescences (cm) 15–25 20–40 15–35 30–39
Stem terete or subterete, 8–18 cm long terete or subterete,1–2 cm long slightly tetragonal, 10–22 cm long tetragonal or subterete, 15–30 cm long
Leaf arrangement evenly spaced along the stem fascicled on short rosette-like stem evenly spaced along the stem evenly spaced along the stem
petiole length (mm) 4–6 0.5 5–10 15–20
blade shape and size (cm) obovate to oval, 6–10 × 2–4 elliptic, oblong-elliptic or obovate, 8.5–15 × 5–9 broadl, lanceolate or obovate-lanceolate, 2–19 × 1.4–8 narrowly elliptic, oblanceolate or elliptic-oblong, 3–12 × 1–4.5
Stipule shape and size (mm) broadly ovate or deltoid, apex cuspidate, margin entire, 2.5–3 × 5–6 triangular, apex acute, margin shortly hairy, 3–5 × 5–10 triangular, apex acute, margin dense trichomes, 4–8 × 5–10 triangular, apex and margin lacerate or deeply divided into several linear lobes, ca. 16 × 8
Inflorescence Longistylous flowers lax or not congested into a head-like inflorescence Longistylous flowers lax or not congested into a head-like inflorescence Longistylous flowers congested into a head-like inflorescence Longistylous flowers congested into cymose or capitate inflorescence
Peduncle length (cm) 2–4 10–18 10 3–4
Lowest floral bracts suborbicular or broadly oval, 2–2.5 × 1.5–2 cm subovate, 2.5–3 × 1.8–2 cm or sometimes larger ovate to lanceolate, 0.6–2.5 × 0.2–1 cm ovate, ca. 1.5 × 0.5–0.6 cm
Calyx lobes ovate or nearly oval, 1.7–2.2 × 0.8–1.4 mm subulate, ca. 1.5 mm long subulate, ca. 3 mm long unknown
Corolla
outer colour bluish purple white purplish white unknown
tube dimension and shape 6–7 × 1–1.5 mm, slightly enlarged both ends ca.3 × 1.5–1.8 mm, slightly narrower near mouth tube ca. 4.5 × 2–2.5 mm, enlarged at mouth unknown
Stamens of long-styled flowers inserted in lower ¼ (or near the base) of corolla tube inserted in upper ¼ (or near the throat) of corolla tube inserted in ½ (or middle) of corolla tube unknown
Stamens of short-styled flowers inserted in the upper ¼ (or near the throat) of corolla tube; inserted near the throat of corolla tube; inserted near base of corolla tube; unknown
filaments ca. 0.2 mm long, not exserted beyond corolla mouth filaments ca. 0.8 mm long, exserted beyond corolla mouth filaments ca. 0.3 mm long, not exserted beyond corolla mouth
Persistent calyx lobes on fruits ovate or nearly oval, 1.8–2.3 × 0.8–1.5 mm, unveined narrowly triangular or subulate, 1.2–2 × 0.5–0.7 mm, unveined narrowly triangular or subulate, 3–4 × ca.1 mm, unveined lanceolate, 3–6 × 1.2–3 mm, veined
Figure 2. 

Hedyotis konhanungensis A habitat B habit C stipule D adaxial and abaxial leaf surfaces E inflorescences top view F long-styled and short-styled flower G infructescence H fruiting branch. Photos by Q.L. Nguyen and B.H. Photos by Quang, from Luan et al. LTA 531.

Description

Perennial herbs, erect, 15–25 cm tall, completely glabrous. Stem simple, rarely branched, terete, 8–18 cm long, 5–7 mm in diam.; internodes 1–1.5 cm long. Leaves 5–7 pairs per stem, decussate, evenly spaced along the stem, abaxial side dark green, adaxial side glossy, dark purple to purplish black; petioles 4–6 mm long; blade flattened, thick, fleshy (subcoriaceous when dried), obovate-lanceolate to nearly oval, 6–10 × 2–4 cm; base decurrent or cuneate; apex broadly acute or obtuse; midrib depressed adaxially and prominent abaxially; 4–5 secondary veins on each side of the midrib, inconspicuous on adaxial side. Stipule interpetiolar, fused to leaf bases or very shortly around stem, broadly ovate or deltoid, 2.5–3 mm long, 5–6 mm wide at base, flattened, dark purple outside; apex cuspidate or aristate, with aristae 3–4 mm long and 0.7–0.9 mm wide; margins entire. Inflorescence terminal, a compound dichasial cyme, 5–7 cm long, with 3–4 orders of branching, purplish, 30–50-flowered. Peduncle terete, 2–4 cm long; bracts subtending the basal branches of the inflorescence leaf-like, suborbicular or broadly oval, slightly concave, 2–2.5 × 1.5–2 cm, with apex rounded to broadly acute or obtuse, abaxially dark purple to dark bluish purple, pale green adaxially; bracts subtending the upper inflorescence branches smaller, ovate or lanceolate, 0.8–1.5 × 0.5–1 cm, with acute apex. Pedicels terete, 3–6 mm long, usually bluish purple or purplish, bracteolate or ebracteolate; bracteoles narrowly ovate or lanceolate, somewhat concave, ca. 2.5 mm × 1.5 mm, with apex broadly acute or obtuse. Flowers 4-merous, distylous. Calyx hypanthium, bluish purple, cupular, 0.8–1.2 mm long and wide, glossy and glabrous; lobes 4, sub-equal, ovate or nearly oval, somewhat longitudinally concave, 1.7–2.2 mm long, 0.8–1.4 mm wide, broadly acute to obtuse at apex, adaxially white or purplish white, abaxially bluish purple. Corolla narrowly infundibuliform or tubular, bluish purple outside, white pubescent inside; tube 6–7 mm long, 1–1.5 mm wide, slightly enlarged at both ends; lobes 4, strongly reflexed, triangular-ovate, 1.5–1.8 × 1.2–1.5 mm, acute, adaxially white or purplish white, sparsely puberulent near base on adaxial surface. Longistylous flowers: stamens inserted in the lower ¼ of corolla tube, 1.5–2 mm above the base of tube; filaments very short, ca. 0.2 mm long; anthers linear, 1–1.2 × 0.2 mm, dorsifixed, introrse; style filiform, 5.5–6.5 mm long, white, glabrous, 2-parted; lobes oblong, 0.6–0.7 mm long, abaxially minutely papillose, pure white, slightly exserted beyond the corolla mouth; ovary inferior, 2-locular, with numerous ovules, placentation axile. Brevistylous flowers: stamens inserted on the upper ¼ of corolla tube, 1–1.5 mm below the corollas mouth; filaments and anthers similar to those in the long-styled flowers; style filiform, 1.5–1.8 mm long, 2-parted; lobes oblong, 0.6–0.7 mm long, densely papillose abaxially. Disks fleshy, ring-shaped, concave in the center, glabrous, white. Fruits capsular, nearly cupuliform with slightly concave top, 2.5–3 mm in diam., glabrous, purplish, crowned by the persistent, unveined, oval or nearly oval calyx lobes. Seeds many, black, irregularly angular, reticulate, minute, 0.3–0.5 mm long.

Figure 3. 

Hedyotis konhanungensis A habit B stipule C inflorescence D floral bracts E bracteoles and fruits F, G calyx top and side views H–K long-styled flower, entire and open showing pistil, corolla and anthers L–P short-styled flower, dissection showing calyx, corolla, anthers and pistil Q–T fruit, entire and dissection U seeds. Photos and design by B.H. Quang from Luan et al. LTA 531.

Additional specimens examined

(Paratypes). Vietnam. Central Highlands of Vietnam. Kon Ha Nung Biosphere Reserve, Central Highlands of Vietnam, Gia Lai province: K’Bang District, Kon Pne Commune, 14°20'43.06"N, 108°20'38.33"E, 906 m a.s.l., 26 March 2022, Bui Hong Quang et al. BHQ 453 (HN, and herbarium of Kon Ka Kinh National Park).

Etymology

This species is named after the “Kon Ha Nung Biosphere Reserve” where it was discovered.

Vernacular name

Vietnamese: An điền Kon Hà Nừng

Phenology

Flowering in October to November, fruiting from November to December.

Distribution and ecology

Hedyotis konhanungensis is recorded only from the type locality in the Kon Pne Commune of the Central Highlands of Vietnam, which is part of the Annamite Range. This range is known for its rich biodiversity and high number of endemic species (Averyanov et al. 2003). The species grows in the understorey of the evergreen forests in the valleys or on flat areas to slopes of sandstone mountains. Within its occupancy areas, the new species was associated with some shrubs or herbs such as Pavetta bauchei Bremek., Lasianthus biflorus (Blume) M.Gangop. & Chakrab., Staurogyne sp., Popowia sp., Huperzia sp.

Discussion

The genus Hedyotis, as currently circumscribed, corresponds to a primarily woody genus characterized by “diplophragmous” capsules (septicidally dehiscent capsules that separate into two distinct valves, as described by Wight and Arnott in 1834) and “fruiticosa type” seeds (dorsiventrally flattened seeds with a ventral hilar ridge topped by a punctiform apical hilum, as described by Terrell and Robinson in 2003). The members of this hyperdiverse genus (approximately 180 species) primarily occupy the mountains of Asia and the Micronesian Islands (in the northwestern Pacific). The molecular dating analysis suggests that Hedyotis split from its sister lineages of approximately 10 species (the African/Malagasy Agathisanthemum group and the African-tropical Asian-North American Edrastima group) nearly 27 million years ago (Neupane et al. 2017). The phylogenetic comparative analysis of evolutionary correlations shows that the evolution and diversification of the hyperdiverse Hedyotis along tropical mountain orogeny are strongly linked to the formation of a woody habit and many narrow endemic species (Neupane et al. 2017). The new species Hedyotis konhanungensis, found in the mountains of central Vietnam, is another example of a tropical montane species in this genus. This species is resolved within the clade containing other southeast Asian species and is unique among the Indochinese Hedyotis in its thick and fleshy oval leaves and completely dark purple floral parts (calyx and corolla) including the inflorescence stalk. Despite the geographic distance, its morphological similarity with Chinese members and non-monophyletic group of H. shenzhenensis and H. shiuyingiae with H. yangchunensis (Fig. 1) suggests the independent evolution of fleshy leaves and somewhat stunted growth habit among these species. Here we provide both morphological and molecular evidence to confirm the novelty of this taxon and propose it as species new to science.

Acknowledgements

The authors gratefully acknowledge the help of the directors, curators and staff of the following herbaria: HN, P, VNM, and VNMN, for allowing access to herbarium specimens and references. The study was supported by the Vietnam Academy of Science and Technology (VAST) under grant number ĐL0000.03/22-23.

References

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Supplementary materials

Supplementary material 1 

Taxa and NCBI GenBank accessions used to estimate phylogeny of Spermacoceae for this study

Bui Hong Quang, Khang Sinh Nguyen, Tuan Anh Le, Le Thi Mai Linh, Quoc Luan Nguyen, Duy Hoang Vu Ngo, Lei Wu, Suman Neupane

Data type: Excel datasheet

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 (38.82 kb)
Supplementary material 2 

A concatenated nexus alignment of four DNA regions (ITS, ETS, petD, rps16) used to estimate phylogeny of Spermacoceae for this study

Bui Hong Quang, Khang Sinh Nguyen, Tuan Anh Le, Le Thi Mai Linh, Quoc Luan Nguyen, Duy Hoang Vu Ngo, Lei Wu, Suman Neupane

Data type: Nexus alignment

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 (1.62 MB)
Supplementary material 3 

Output of RAxML tree analysis with bootstrap values (1000 replicates)

Bui Hong Quang, Khang Sinh Nguyen, Tuan Anh Le, Le Thi Mai Linh, Quoc Luan Nguyen, Duy Hoang Vu Ngo, Lei Wu, Suman Neupane

Data type: Newick tree file

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 (28.69 kb)
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