Taxonomic studies on the genus Isotrema (Aristolochiaceae) from China: II. I. brevilimbum (Aristolochiaceae), a new species from Guizhou, China

Jun Wang; Ji-Dong Ya; Cheng Liu; Guang Liu; Feng Cao; Jin-Shuang Ma; Xin-Xin Zhu

doi:10.3897/phytokeys.152.51760

Research Article

Taxonomic studies on the genus Isotrema (Aristolochiaceae) from China: II. I. brevilimbum (Aristolochiaceae), a new species from Guizhou, China

Jun Wang^‡, Ji-Dong Ya^§, Cheng Liu^§, Guang Liu^|, Feng Cao^¶, Jin-Shuang Ma^#, Xin-Xin Zhu^‡

‡ Xinyang Normal University, Henan, China

§ Kunming Institute of Botany, Yunnan, China

| Haizhu District Experimental Primary School, Guangzhou, China

¶ Unaffiliated, Guizhou, China

# Chinese Academy of Sciences, Shanghai, China

Corresponding author: Jin-Shuang Ma ( jinshuangma@gmail.com )

Corresponding author: Xin-Xin Zhu ( zhuzhu8niuniu@126.com )

Academic editor: Elton John de Lirio

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: Wang J, Ya J-D, Liu C, Liu G, Cao F, Ma J-S, Zhu X-X (2020) Taxonomic studies on the genus Isotrema (Aristolochiaceae) from China: II. I. brevilimbum (Aristolochiaceae), a new species from Guizhou, China. PhytoKeys 152: 15-25. https://doi.org/10.3897/phytokeys.152.51760

Abstract

A new species of Isotrema was recently discovered from Guizhou, China and is here named as I. brevilimbum. It is most similar to I. ovatifolium and I. wardianum, but differs in the morphology of leaves and flowers. A detailed description for the new species, along with line drawings, photographs, as well as morphological comparisons with similar species, are provided. In addition, the distribution of I. wardianum in China is here confirmed.

Keywords

Aristolochia wardiana, morphology, subgenus Siphisia, taxonomy

Introduction

Isotrema Raf. (Aristolochiaceae), previously treated as a subgenus of Aristolochia L., was recently reinstated as an independent genus based on molecular and morphological evidence (Zhu et al. 2019a). It can be distinguished from Aristolochia by the following set of characters: perianth strongly curved, gynostemium 3-lobed, anthers paired on the outer surface of each gynostemium segment, and capsule dehiscing basipetally (Do et al. 2015a; Zhu et al. 2019a). Several new species of Isotrema have been found and described from China and its neighbouring countries during recent years (Liu and Deng 2009; Xu et al. 2011; Yao 2012; Huang et al. 2013, 2015; Wu et al. 2013, 2015; Do et al. 2014, 2015a, 2015b, 2015c, 2015d, 2016, 2017, 2019; Huong et al. 2014; Lu and Wang 2014; Ohi-Toma et al. 2014; Zhu et al. 2015, 2016, 2017a, 2017b, 2018, 2019b, 2019c; Gong et al. 2018; Yang et al. 2018; Li et al. 2019; Peng et al. 2019; Zhou et al. 2019; Cai et al. 2020a, 2020b). Currently, a total of 106 species have been reported from Isotrema, most of which are distributed in eastern and southern Asia, with some species further extended to northern and central America (Zhu et al. 2019a). China accommodates ca. 66 species, among which 55 species are endemic (Huang et al. 2003; Li et al. 2019; Peng et al. 2019; Zhou et al. 2019; Zhu et al. 2019a, 2019b, 2019c, 2019d; Cai et al. 2020a, 2020b).

During our recent field explorations to southern China, an unknown species of Isotrema was collected. Our subsequent examination of specimens from 39 public herbaria (A, BM, BR, CDBI, CSFI, CSH, E, EMA, GXMI, HAST, HENU, HHBG, HIB, HITBC, HNWP, IBK, IBSC, K, KYO, KUN, L, LBG, LE, NAS, NTUF, P, PE, PEM, SM, SNU, SYS, TAI, TI, W, WCU, WU, WUK, XYTC, YUKU; abbreviations follow Thiers 2020) and study of related literature (Hwang 1981, 1988; Ma 1989a, 1989b; Tao 1997; Huang et al. 2003; Do et al. 2015a; Do and Nghiem 2017; Yang et al. 2018; Zhu et al. 2019a, 2019d) suggested it to be a new species. Hereafter, we describe it as I. brevilimbum X.X.Zhu, Jun Wang & F.Cao. Moreover, I. wardianum (J.S. Ma) X.X. Zhu, S. Liao & J.S. Ma was recently published (Zhu et al. 2019a) based on its basionym A. wardiana J.S. Ma, previously only known from Myanmar and India (Ma 1989a), which was recently collected from Medog County, Tibet, and here its distribution in China is confirmed. Measurements and morphological characters of I. brevilimbum, I. ovatifolium and I. wardianum were made from both dried specimens and field observations of living plants, as well as including related literature. The morphological characters of the description follow Huang et al. (2003).

Taxonomy

Isotrema brevilimbum X.X.Zhu, Jun Wang & F.Cao, sp. nov.

urn:lsid:ipni.org:names:77209990-1

Figures 1, 2A–F, 3, 4A–C, 5

Type

China. Guizhou: Weining County, Jinzhong Town, 2226 m alt., 5 Aug 2018, X.X. Zhu et al. ZXX18217 (holotype: CSH–0172289!; isotypes: CSH!, KUN!).

Diagnosis

Isotrema brevilimbum is morphologically similar to I. ovatifolium (S.M. Hwang) X.X. Zhu, S. Liao & J.S. Ma and I. wardianum (J.S. Ma) X.X. Zhu, S. Liao & J.S. Ma, but differs from the former in its lamina long ovate (vs. lamina ovate in I. ovatifolium), perianth limb forming right angle with upper tube, length nearly equal to width, and apex dark purple and opened (vs. limb straightly extended from upper tube, length significantly longer than width, and apex dark purple and constricted in I. ovatifolium), differs from the latter in its lamina long ovate and abaxially densely villous (vs. lamina lanceolate and abaxially subglabrous or glabrous in I. wardianum), perianth limb forming right angle with upper tube, length nearly equal to width, and apex dark purple and opened (vs. limb forming obtuse angle with upper tube, length significantly longer than width, and apex light yellow and constricted in I. wardianum).

Figure 1.

Isotrema brevilimbum X.X.Zhu, Jun Wang & F.Cao. A Branch B leaf C, D flower E longitudinal–section of flower (showing inside structure) F anthers and gynostemium G capsule H seed. Drawn by S.Z. Qiao.

Description

Climbing shrubs. Stems terete, densely villous when young, old branchlets glabrous. Petioles 1–4 cm long, densely villous; laminas long ovate, 5–13 × 2.5–3.5 cm, adaxially appressed villous, abaxially densely villous, base cordate, margin entire, apex acute; basal veins palmate, 2–3 pairs from base, lateral veins 4–6-paired. Flowers axillary or lateral on young stems, solitary, rarely paired. Pedicels pendulous, 1.5–3 cm long, densely villous; bracteole ovate, conduplicate, ca. 2 × 1 mm, abaxially densely villous, adaxially smooth, inserted on lower part of pedicel. Perianth tube geniculately curved, abaxially villous; basal tube ca. 1 cm long, inside dark red, upper tube ca. 1.5 cm long, inside red; limb short cylinder, length nearly equal to width, ca. 7 × 8 mm, forming right angle with upper tube, apex dark purple, opened, ca. 7 mm wide at mouth, inside dark red with densely tiny dark-purple papillae; throat subcircular, ca. 4 mm wide. Anthers 6, oblong, ca.1.5 mm long, adnate in 3 pairs to base of gynostemium, opposite to lobes. Gynostemium ca. 3 mm long, 3-lobed. Ovary terete, ca. 8 mm long, densely villous. Capsule cylindric, abaxially densely villous, ca. 4.5 × 2 cm. Seeds ovate, 4–5 × 3–3.5 mm, concave-convex.

Figure 2.

A–F Isotrema brevilimbum X.X.Zhu, Jun Wang & F.Cao. A Habitat B leaves C lateral view of flower D frontal view of flower E anthers and gynostemium F capsule G–I I. wardianum G habit H frontal view of flower I anthers and gynostemium. A Photographed by F. Cao B, E, F photographed by X.X. Zhu C, D photographed by G. Liu G photographed by C. Liu H, I photographed by J.D. Ya.

Phenology

Flowering from May to August, fruiting from July to September.

Etymology

The specific epithet refers to the short cylinder perianth limb of the new species. The “brevi” means “short”, “limbum” means “limb”, so the new species is named Isotrema brevilimbum.

Figure 3.

Holotype of Isotrema brevilimbum X.X.Zhu, Jun Wang & F.Cao (CSH–0172289).

Common name (assigned here)

Duan Yan Guan Mu Tong (短檐关木通; Chinese name).

Distribution and habitat

The new species is currently only known from Weining County of Guizhou, China. It grows by the roadside of farmland at an altitude of ca. 2200 m.

Figure 4.

Leaves, lateral view of flowers, and longitudinal dissected flowers of Isotrema brevilimbum (A–C), I. ovatifolium (D–F), and I. wardianum (G–I). A–F Photographed by X.X. Zhu G photographed by C. Liu H, I photographed by J.D. Ya.

Preliminary conservation status

Isotrema brevilimbum is known from a single population including two individuals on the roadside of farmland. The new species is assigned a preliminary status of vulnerable (VU) according to the IUCN Red List Categories (IUCN 2012). However, since very few details exist about its natural distribution, the lack of sufficient data currently does not allow a final risk evaluation and the species might be regarded as data deficient (DD). Further field surveys in western Guizhou and northeastern Yunnan are needed to gain more information on its distribution. Not only is the area not under protection as a nature reserve, but also habitat disturbance brought about by human activities, such as grazing and farming, may have a negative impact on the new species.

Note

Isotrema wardianum was previously only known from Myanmar and India. Sun and Zhou (2002) later reported the species from China, according to a specimen collected from Medog County of Tibet (H. Sun et al. 4935), but without flower or fruit. Nevertheless, the species had long been neglected by taxonomic studies of Huang et al. (2003), Do et al. (2015a), and Zhu et al. (2019a, 2019d) on Chinese Isotrema. It was not until 2018 that we discovered a seedling of Isotrema sp. at the same locality as that of H. Sun et al. 4935 and transplanted it in the nursery of the Kunming Institute of Botany. A year later, the plant grown from this seedling bloomed and enabled us to identify it as I. wardianum (Figs 2G–I, 4G–I) and confirm its distribution in China.

Figure 5.

Distribution of Isotrema brevilimbum, I. ovatifolium, and I. wardianum based on field observation, specimens and literatures examined.

Discussion

Isotrema brevilimbum is morphologically similar to I. ovatifolium and I. wardianum in the shape, size, and color of flower and the dark-purple papillae in the inner surface of perianth limb, but they can be distinguished by the morphology of lamina, the angle between perianth limb and upper tube, as well as the length and mouth of limb. Detailed morphological comparisons among the three species are summarized in Table 1 and Fig. 4.

Table 1.

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XLSX

Morphological comparisons among Isotrema brevilimbum, I. ovatifolium and I. wardianum. These characters were based on field observation, related specimens and literatures (Hwang 1981; Ma 1989a; Huang et al. 2003).

Characters	I. brevilimbum	I. ovatifolium	I. wardianum
Lamina	long ovate, 5–13 × 2.5–3.5 cm, abaxially densely villous, base cordate	ovate, 5–13 × 4–8 cm, abaxially densely villous, base cordate	lanceolate, 12–16 × 3–4 cm, abaxially subglabrous or glabrous, base auriculate
Perianth limb	short cylinder, forming right angle with upper tube, length nearly equal to width, apex dark purple, opened, ca. 7 mm wide at mouth	cylinder, straightly extended from upper tube, length significantly longer than width, apex dark purple, constricted, ca. 1 mm wide at mouth	cylinder, forming obtuse angle with upper tube, length significantly longer than width, apex light yellow, constricted, ca. 3 mm wide at mouth
Perianth throat	ca. 4 mm wide	ca. 2.5 mm wide	ca. 2 mm wide
Anthers	ca. 1.5 mm long	ca. 1.5 mm long	ca. 2 mm long
Gynostemium	ca. 3 mm long	ca. 3.5 mm long	ca. 3.5 mm long
Capsule	ca. 4.5 × 2 cm	ca. 6 × 2 cm	unknown
Distribution	China (Guizhou)	China (Guizhou, Sichuan, Yunnan)	China, Myanmar, India

Specimens of Isotrema wardianum examined. Myanmar. Adung Valley, 12 Apr 1931, F. Kingdon-Ward 9398 (holotype: BM). China. Tibet: Medog County, 2100 m, 21 Mar 1993, H. Sun et al. 4935 (KUN); at the same locality, 1705 m, 27 Nov 2018, C. Liu & J.D. Ya 18CS17145 (KUN).

Specimens of Isotrema ovatifolium examined. China. Guizhou: Weining County, Jinzhong Town, 2232 m, 5 Aug 2018, Zhu et al. ZXX18218 (CSH, KUN); Sichuan: Huidong County, 2520 m, 27 Jun 1959, S.K. Wu 1584 (type: SM).

Acknowledgements

The authors are very grateful to Ms. Shi-Zhen Qiao for the line drawing of I. brevilimbum. This study was jointly supported by the National Natural Science Foundation of China (grant nos. 31600161 and 31370225), the Nanhu Scholars Program for Young Scholars of XYNU, and the Institute for Conservation and Utilization of Agro-bioresources in the Dabie Mountains.

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