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Research Article
Mazus danxiacola (Mazaceae), a distinct new species endemic to Danxia landform in Jiangxi Province, eastern China
expand article infoBo Li§, Xin-Gui Le|, Dao-Zhang Min, Lin Xu|, Bin Chen
‡ Jiangxi Agricultural University, Nanchang, China
§ Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, China
| Yangjifeng National Nature Reserve Administration of Jiangxi Province, Guixi, China
¶ Shanghai Chenshan Botanical Garden, Shanghai, China
Open Access

Abstract

Mazus danxiacola, a new species endemic to Danxia landform in east Jiangxi Province, eastern China, is described and illustrated. The systematic placement of this new species was confirmed by molecular phylogenetic analyses based on four plastid markers (matK, rbcL, rps16 and trnL-trnF) and nuclear ribosome ITS sequence, and its specific relationships within Mazus were discussed. Morphologically, the new species is clearly different from other Mazus species by having a series of uncommon traits, i.e., annual habit, without stolons and basal leaves, single, erect and unbranched stems, long petiolate leaves abaxially grayish green to silver gray, truncate to broadly cuneate leaf bases, racemes extremely elongated up to 35 cm long, white corolla, and palate densely covered by conspicuous clavate gland-like hairs. The new species is assigned to Critically Endangered (CR) according to the IUCN Red List Categories and Criteria.

Keywords

cpDNA, Lamiales, molecular phylogenetics, morphology, nrITS

Introduction

Mazaceae (Reveal 2011) is a newly established small family that was separated from the traditionally circumscribed Scrophulariaceae (e.g., Von Wettstein 1891; Thieret 1967; Fischer 2004). There are four genera currently recognized in the family: Dodartia L., Lancea Hook.f. & Thomson, Mazus Lour, and Puchiumazus Bo Li, D.G. Zhang & C.L. Xiang (Stevens 2001 onwards; Xiang et al. 2021). Among these, Dodartia, Lancea and Puchiumazus contains only sole or two species (Fischer 2004; Deng et al. 2019; Xiang et al. 2021), while Mazus includes 37 accepted species which are distributed mainly in Asia to Australasia (POWO 2022). Nearly all species of Mazus are annual or perennial herbs (Hong et al. 1998; Deng et al. 2016), except the M. fruticosus Bo Li, D.G. Zhang & C.L. Xiang which was recently described as a new species having a shrubby habit (Xiang et al. 2021). Mazus is characterized by a combination of morphological characters: a strongly two-lipped corolla (3/2-bilabiatae), a palate with two longitudinal plaits and a capsule enclosed in a persistent calyx (Fischer 2004; Deng et al. 2019). In China, 25 species and three varieties were recorded in the Flora of China (FOC, Hong et al. 1998), but new species were continuously reported since the publication of the FOC, i.e., M. tainanensis T.H. Hsieh (Hsieh 2000), M. sunhangii D.G. Zhang & T. Deng (Deng et al. 2016), M. somggangensis S.S. Ying (Ying 2019), M. fruticosus (Xiang et al. 2021), etc., indicating that there is probably a hidden diversity of Mazus in China that needs to be revealed.

In 2021, during a special botanical survey for the Danxia landforms in Jiangxi Province, eastern China, the authors encountered two populations of an unusual species of Mazus in Guixi City, eastern Jiangxi. The unknown plant is an annual herb having a single erect unbranched stem, no rosulate basal leaves, stem leaves many and alternate with long petioles up to 4.5 cm, abaxial leaf surface grayish green to silver gray, raceme extremely elongated up to 35 cm and densely pubescent and glandular hairs, white corolla with the palate densely covering conspicuous and clavate gland-like hairs (Fig. 1). After checking and comparing the plant with all known congeneric taxa, we conclude that it represents a distinct undescribed new species of Mazus, M. danxiacola, which is described in the present study.

Figure 1. 

Morphology of Mazus danxiacola sp. nov. A habitat B seedlings C habit D a flowering individual E fruiting specimens F roots G fruit H leaves I a mature inflorescence with flowers and fruits J young inflorescence, showing dense pubescence and glandular hairs K flower (lateral view) L palate, showing the conspicuously long and clavate gland-like hairs. Scale bars: 2 cm (B, H); 5 cm (C); 1 cm (F, I); 2 mm (G, J, K, L).

Materials and methods

Field investigations were carried out in Danxia mountains of Guixi City, Jiangxi Province from May to October in 2021. Voucher specimens in flowering and fruiting were collected in the field in June and August, respectively. All specimens were deposited in the herbarium of Shanghai Chenshan Botanical Garden (CSH) and voucher photos taken in situ were deposited in the “Chinese Field Herbarium” (https://www.cfh.ac.cn/album/ShowSpAlbum.aspx?spid=94285).

The morphological description of the putative new species was conducted based on observations and measurements of mature plants in field as well as specimens. Measurements were taken using a ruler and a vernier caliper. Herbarium specimens of other Mazus species in China were examined via the Chinese Virtual Herbarium (https://www.cvh.ac.cn/) and National Specimen Information Infrastructure (http://www.nsii.org.cn/2017/home.php) platforms. High resolution images of the type specimens of Mazus were consulted on JSTOR Global Plants (http://about.jstor.org/). The conservation status of the new species was evaluated based on the guidelines of the IUCN Red List categories and criteria (IUCN 2022).

In order to confirm the systematic placement of the putative new species within Mazus, molecular phylogenetic analyses were conducted following the procedures presented in Xiang et al. (2021). The combined cpDNA dataset (matK, rbcL, rps16 and trnL-trnF) and the nrITS dataset used in Xiang et al. (2021) were employed with the addition of two individuals (B.Chen CB06425 and B.Chen CB05735) of the putative new species. The two datasets were simplified and adjusted to set the species of Mazus as ingroups (22 and 17 species in cpDNA and nrITS datasets, respectively) and Dodartia orientalis L. and Lancea tibetica Hook. f. & Thomson were selected as outgroups based on previous phylogenies (Deng et al. 2019; Xiang et al. 2021). Methods of DNA extraction, amplification, sequencing, and phylogenetic analyses using maximum likelihood (ML) and Bayesian inference (BI) follow those presented in Deng et al. (2019) and Xiang et al. (2021). Voucher information and GenBank accession numbers for taxa used in this study are provided in Table 1.

Table 1.

Taxa, GenBank accession numbers of DNA sequences, and their vouchers used in this study. Newly sequenced taxa are shown in bold, and missing data are indicated by a dash (-).

Taxa matK Voucher rbcL voucher rps16 voucher trnL-F voucher ITS voucher
Dodartia orientalis L. MK392230 XZ-2008-1 JQ342984 XZ-2008-1 JQ342982 XZ-2008-1 JQ342981 XZ-2008-1 JQ342980 XZ-2008-1
Lancea tibetica Hook. f. & Thomson MF786907 Tibet-MacArthur2276 MF786661 Tibet-MacArthur2276 FJ172699 XZ-2007-0525 FJ172685 XZ-2007-0525 FJ172736 XZ-2007-0525
Mazus alpinus Masam. MK266256 Sunhang11307 KX783481 Sunhang11307 KX783501 Sunhang11307 KX783520 Sunhang11307 MK192641 Sunhang11307
M. caducifer Hance MK266277 KUN35025 KX783477 KUN35025 KX783497 KUN35025 KX783516 KUN35025 MK192664 KUN35025
M. celsioides Hand.-Mazz. KX783486 YIF0093 MK266366 YIF0093 KX783525 YIF0093
M. danxiacola Bo Li & B. Chen 1 ON323563 CB06425 ON323565 CB06425 ON323567 CB06425 ON323569 CB06425 ON286711 CB06425
M. danxiacola Bo Li & B. Chen 2 ON323564 CB05735 ON323566 CB05735 ON323568 CB05735 ON323570 CB05735 ON303604 CB05735
M. fauriei Bonati KX783479 Sunhang11248 KX783499 Sunhang11248 KX783518 Sunhang11248 LC034207 HUP97
M. gracilis Hemsl. FJ172729 XZ-2007-058 FJ172701 XZ-2007-058 FJ172687 XZ-2007-058 FJ172738 XZ-2007-058
M. fruticosus Bo Li, D.G. Zhang & C.L. Xiang MK266261 zdg4447 KX783470 zdg4447 KX783490 zdg4447 KX783509 zdg4447 MK192660 zdg4447
M. humilis Hand.-Mazz. MK266367 dt149 MK266421 dt149 MK192667 dt149
M. longipes Bonati MK266267 Deng1941 KX783474 Deng1941 KX783494 Deng1941 KX783513 Deng1941 MK192652 Deng1941
M. miquelii Makino NC_056339 Zeng et al. (2021) NC_056339 Zeng et al. (2021) NC_056339 Zeng et al. (2021) NC_056339 Zeng et al. (2021) LC027734 Maruyama:sn
M. novaezeelandiae W.R. Barker MK266278 dtA68 KX783469 dtA68 KX783489 dtA68 KX783508 dtA68 MK192676 dtA68
M. omeiensis H.L. Li MK266252 nie1976 KX807209 nie1976 KX807203 nie1976 KX807208 nie1976 MK192636 nie1976
M. procumbens Hemsl. MK266261 zdg6074 KX783478 zdg6074 KX783498 zdg6074 KX783517 zdg6074 MK192647 zdg6074
M. pulchellus Hemsl. KX783472 dt093 KX783492 dt093 KX783511 dt093 MK192638 dt093
M. pumilio R. Br. MK266277 Pagest.s.n.2021829 KX783468 Pagest.s.n.2021829 KX783488 Pagest.s.n.2021829 KX783507 Pagest.s.n.2021829 MK192671 Pagest.s.n.2021829
M. pumilus (Burm. f.) Steenis MK266259 XZ-2007-051 FJ172728 XZ-2007-051 FJ172700 XZ-2007-051 FJ172686 XZ-2007-051 FJ172737 XZ-2007-051
M. pumilus var. delavayi (Bonati) T.L. Chin ex D.Y. Hong MK266257 Sunhang11459 KX783482 Sunhang11459 KX783502 Sunhang11459 KX783521 Sunhang11459
M. radicans Cheesman KT626738 CHR618785 MK266381 CHR618785 MK192635 CHR618785
M. spicatus Vaniot MK266251 XZ-2007-0514 FJ172730 XZ-2007-0514 FJ172703 XZ-2007-0514 FJ172689 XZ-2007-0514 FJ172740 XZ-2007-0514
M. sunhangii D.G. Zhang & T. Deng KX783484 zdg4142 KX783504 zdg4142 KX783523 zdg4142
M. surculosus D. Don KX783473 KUN0472212 KX783493 KUN0472212 KX783512 KUN0472212
M. xiuningensis X.H. Guo & X.L. Liu NC_056340 Zeng et al. (2021) NC_056340 Zeng et al. (2021) NC_056340 Zeng et al. (2021) NC_056340 Zeng et al. (2021)

Results

Phylogenetic analysis

The combined cpDNA dataset has 25 aligned sequences and comprise 3851 characters (860 bp for matK, 1267 bp for rbcL, 837 bp for rps16, and 887bp for trnL-trnF, respectively), of which 327 are variable (8.49%) and 225 are parsimony-informative (5.84%). The nrITS dataset has 20 sequences with the aligned length of 609 bp, of which 176 are variable (28.90%) and 142 are parsimony-informative (23.32%). Phylogenetic analyses based on the two datasets were conducted separately because the taxon sampling is different in these datasets. ML and BI trees generated from each dataset yielded similar topologies, thus only the ML trees are presented (Figs 2, 3). In all analyses, the monophyly of Mazus was strongly supported (Figs 2, 3; cpDNA tree: ML-BS=100%, BI-PP=1.00; nrITS tree: ML-BS=100%, BI-PP=1.00; all values reported in this order below), and the two individuals of M. danxiacola formed a highly supported clade (99%, 1.00; 99%, 0.99), which was consistently nested within Mazus in both cpDNA and nrITS trees. However, specific relationships within the genus were not fully resolved. In the cpDNA tree, M. danxiacola was sister to M. fauriei Bonati with moderate supports (Fig. 2; 83%, 0.99), while in the nrITS tree, M. danxiacola was sister to a clade comprising M. pumilis (N.L. Burman) Steenis and M. gracilis Hemsl. (100%, 1.00), and they together obtained highly supported values (100%, 1.00).

Figure 2. 

Maximum Likelihood phylogram of Mazus as inferred from analysis of combined dataset of matK, rbcL, rps16 and trnL-trnF. Support values ≥ 50% BS or 0.90 PP are displayed above and below the branches, respectively.

Figure 3. 

Maximum Likelihood phylogram of Mazus as inferred from analysis of nrITS dataset. Support values ≥ 50% BS or 0.90 PP are displayed above and below the branches, respectively.

Taxonomic treatment

Mazus danxiacola Bo Li & B. Chen, sp. nov.

Fig. 1

Diagnosis

This species is distinct from all currently known congeneric species and could be easily distinguishable by its annual habit, single, erect and unbranched stems, long petiolate leaves with truncate to broadly cuneate base and grayish green to silver gray lower surface, terminal racemes up to 35 cm long, white corolla with the palate densely covering conspicuous clavate gland-like hairs and having no stolons and basal leaves.

Type

China. Jiangxi Province: Guixi City, Liukou town, under the cliffs of Danxia mountains, alt. 75m a.s.l., 12 June 2021, Bin Chen CB05735 (holotype CSH!, barcode CSH0186434; isotypes CSH!, barcode CSH0186431, CSH0186433, CSH0118470); in the same location of holotype, 24 August 2021, Xingui Le & Lin Xu CSH42465 (paratype CSH!, barcode CSH0188116).

Description

Annual herbs, 15–65 cm tall, without stolons. Primary roots thick and strong; adventitious roots numerous, shotting from the stem base, white and slightly freshy. Stems single, erect, unbranched, terete; old stems purplish brown, sparsely puberulent; young stems grayish green, densely villous and sparsely glandular hairy. Leaves all cauline, numerous, alternate, long petiolate, larger at middle of stem; petioles densely puberulent to subglabrous, 1.5–4.5 cm long; leaf blade broadly ovate to suborbicular, membranous, 2.5–5.3 × 2.3–4.8 cm, adaxially green, subglabrous to sparsely puberulent, abaxially grayish green to silver gray, subglabrous, densely villous on veins, apex obtuse to rounded, base truncate to broadly cuneate, margin crenate, teeth apices callous, sometimes with 1 or 2 pairs of lobes near base; veins conspicuous on both surface, elevated abaxially, fluted adaxially. Racemes terminal or occasionally axillary on the top 1–3 nodes, shortened when young but elongated up to 35 cm long when fruiting, lax, multiflowered; pedicels slender, 0.8–2.5 cm long, densely villous and glandular hairy. Calyces broadly campanulate, 3.0–4.0 mm long, 5-veined, densely villous and glandular hairy outside, subglabrous inside; lobes 5, ovate-triangular, longer than the tube, apex acute, midrib conspicuous, lateral veins inconspicuous. Corolla white, dotted yellow on palate, 0.9–1.2 cm long, sparsely minutely puberulent to glabrous outside, tube cylindric, 0.4–0.6 cm long, exserted from calyx; limb 2-lipped, upper lip bilobed, upwarp, lobes lanceolate; lower lip trilobed, middle lobe narrowly ovate, ca. 1.5 mm long, smaller than lateral lobes, lateral lobes spreading away from middle lobes, broadly ovate to rectangular; palate comprising 2 longitudinal elevations extending from point of filament fusion to base of lower lobes, densely covered by gland-like hairs, hairs clavate and conspicuous, ca. 0.7 mm long, white to transparent. Stamens 4, didynamous, glabrous, inserted at the same level in distal part of tube, included; anterior pair longer, curved, appressed to corolla tube, posterior pair spreading; anthers bithecal, positioned adjacent to corolla tube on upper lip; filaments filiform, glabrous. Styles 0.4–0.5 cm long, included, exserted beyond anthers, stigma 2-lamellate. Capsule globose, ca. 2.5 mm in diam, apex rounded, included by persistent calyx.

Phenology

Flowering was observed from early June to late August and fruiting from June to late September.

Distribution and habitat

The species is currently known only from the type locality of Danxia mountains in Liukou Town of Guixi City, eastern Jiangxi Province, China (Fig. 4), and grows under shaded cliffs and near the edges of subtropical evergreen broad-leaved forests, at an elevation about 75 m a.s.l. (Figs 1A, 5).

Figure 4. 

Distribution map of Mazus danxiacola sp. nov.

Figure 5. 

Danxia landform of the type locality of Mazus danxiacola sp. nov. (left) and the habitat of the new species under a cliff (right). Arrows show where the population could be found.

Etymology

The specific epithet “danxiacola” refers to the species inhabiting in Danxia landform.

Vernacular name

Simplified Chinese: 丹霞通泉草; Chinese pinyin: Dān Xiá Tōng Quán Căo.

Provisional conservation status

Based on our special botanical surveys for Danxia landforms in Jiangxi Province in 2021, M. danxiacola has been discovered only from one single locality so far in Liukou Town of Guixi City in Jiangxi Province, China, and 2 populations were found in the locality, which totally occupied ca. 200 m2. In these populations, a total of ca. 80 fruiting individuals were counted in August 2021 and there were a lot of seedlings in each of the population when we firstly encountered the species in June 2021 (Fig. 1B, C), indicating that the species has a well-developed reproductive strategy in the habitat of Danxia landform. However, the locality is close to downtown of Guixi City, has not been projected to a nature reserve yet and all populations are obviously facing man-made interferences, such as deforestation, touring and grazing, we thus propose to categorize the species as critically endangered (CR) under criteria B and D following IUCN Red List Categories (IUCN 2022).

Taxonomic note

Morphologically, M. danxiacola bears a series of rare traits which are not common in Mazus, such as annual habit, single erect unbranched stems, without basal leaves, stem leaves many and alternate, extremely long petioles up to 4.5 cm, abaxial leaf surface grayish green to silver gray, and palate of corolla densely covered by conspicuously clavate gland-like hairs. The combination of these traits makes M. danxiacola distinct from all other congeneric taxa. Our molecular phylogenetic analyses based on cpDNA dataset indicated that M. fauriei may be closely related to M. danxiacola (Fig. 2), but M. fauriei is a perennial herb with all leaves basal and rosulate and petioles broadly winged (Hong et al. 1998), which is apparently different from M. danxiacola that has only cauline leaves and long unwinged petioles. In the nrITS trees, M. pumilis and M. gracilis were shown as possible alliances of M. danxiacola, however, cauline leaves of the former two species are always opposite, and their basal and cauline leaves are all decurrent to form short petioles (Hong et al. 1998), clearly differing from those alternate and long petiolate leaves of M. danxiacola. It is worth mentioning that there are obvious conflicts between the cpDNA and nrITS phylogenies which have been discovered and discussed in a previous study (Xiang et al. 2021). In fact, the available molecular data of Mazus were not sufficient enough to represent all known species of the genus, thus it is hard to definitely confirm the closest relatives of M. danxiacola at the moment through molecular phylogenetics. Future molecular studies including more species at population level and using more DNA markers may shed light on the determination of specific relationships within Mazus.

So far, M. danxiacola is the first species of Mazus that was found to be endemic to Danxia landform. Danxia landform is a unique type of petrographic geomorphology found in southeast, southwest, and northwest China with a high level of floral endemism (Liu et al. 1999; Liu and Liu 2003; Luo et al. 2010). In southeast China, Danxia landforms are well developed in Guangdong, Fujian, Jiangxi, and Hunan provinces, and the special environment, including deep valleys, grooves, moist caves, cliffy rocks, dry cliff-tops and shaded rock bottoms (Fig. 5), has significant effects on the growth of special plants (Chen et al. 2008). Just in the last ten years, a lot of new taxa have been continuously discovered from Danxia mountains of these provinces, i.e., Danxiaorchis J.W. Zhai, F.W. Xing & Z.J. Liu (Zhai et al. 2013), Spiradiclis danxiashanensis R.J. Wang (Wang et al. 2015), Viola hybanthoides W.B. Liao & Q. Fan (Fan et al. 2015), Begonia danxiaensis D.K. Tian & X.L. Yu (Tian et al. 2019), Phyllostachys danxiashanensis N.H. Xia & X.R. Zheng (Zheng et al. 2019), Semiaquilegia danxiashanensis L. Wu, J.J. Zhou, Qiang Zhang & W.S. Deng (Zhou et al. 2019), Lespedeza danxiaensis Q. Fan, W.Y. Zhao & K.W. Jiang (Zhao et al. 2021), Asplenium danxiaense K.W. Xu et al. (2022), etc., indicating that it is valuable to strengthen the flora investigations in Danxia landforms and uncover the biodiversity.

Acknowledgements

The authors are grateful to administrators and staff of Yangjifeng National Nature Reserve of Jiangxi Province for offering kind assistance during field surveys. This work was supported by the National Natural Science Foundation of China (grant no. 31900181).

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