Taxonomic studies on the genus Isotrema (Aristolochiaceae) from China III: I.pseudohei, a new species from Yunnan, Southwest China

Abstract Isotremapseudohei, a new species from Yunnan, Southwest China, is described and illustrated. It is morphologically similar to I.hei and I.moupinense, but differs from the former in the colour of flower and throat, the size of throat and the shape of gynostemium lobes, and from the latter in the shape of lamina and gynostemium lobes.


Introduction
Isotrema Raf. was previously treated as a subgenus of Aristolochia L. and was recently reinstated as an independent genus base on both molecular data and morphological evidence (Zhu et al. 2019a). It can be distinguished from the genus Aristolochia in the strongly curved perianth with a 3-lobed limb, and especially the 3-lobed gynostemium with a pair of anthers on the outer surface of each gynostemium segment. Comprising 109 species, the genus mainly occurring in East and South Asia, with a few species disjunctly distributed in North and Central America (Zhu et al. 2019a). Currently, 71 species of Isotrema are recorded in China, of which 57 are endemic (Hwang et al. 2003;Lai et al. 2019;Li et al. 2019;Peng et al. 2019;Zhou et al. 2019;Zhu et al. 2019aZhu et al. , 2019bZhu et al. , 2019cZhu et al. , 2019dCai et al. 2020aCai et al. , 2020bLuo et al. 2020;Wang et al. 2020aWang et al. , 2020bLiao et al. 2021).
During a field expedition to Yunnan, Southwest China, some unknown specimens of Isotrema were discovered. After careful comparison with previously known species and study of related literature (Hwang 1988;Ma 1989aMa , 1989bTao 1997;Hwang et al. 2003;Do et al. 2015;Do and Nghiem 2017;Yang et al. 2018;Zhu et al. 2019aZhu et al. , 2019dCai et al. 2020aCai et al. , 2020bWang et al. 2020aWang et al. , 2020b, we confirm it as a new species, describe and illustrate it below.

Material and methods
Specimens of Isotrema from 36 herbaria (A, BM, BR, CDBI, CSFI, CSH, E, EMA, GXMI, HAST, HENU, HHBG, HIB, HITBC, IBK, IBSC, K, KUN, L, LBG, LE, NAS, NTUF, P, PE, PEM, QTPMB, SM, SNU, SYS, TAI, W, WCU, WU, WUK, YUKU; acronyms follow Thiers 2021) and our collections in the field all over Asia were examined. Meanwhile, the literature, in particular the protologues of published names, was collated and reviewed. The geographic distribution has been compiled from literatures and complemented by the analyzed specimens and color photos. Photographs of plants were taken in the wild for each species and the terminology of description was mainly based on the Flora of China (Hwang et al. 2003 Diagnosis. Similar to Isostrema hei Lei Cai & X.X.Zhu and I. moupinense (Franch.) X.X.Zhu, S. Liao & J.S.Ma, but significantly differs in the following characters: laminas lanceolate to narrowly lanceolate, basal tube of calyx ca. 1.5 cm long, inside dark purple at base and yellowish white above base; upper tube of calyx ca. 2.3 cm long, inside yellowish white, getting yellow in upper portion; inner surface of limb yellow with purplish red patches; throat yellow, suborbicular, 7-9 mm in diameter; apex of gynostemium lobes acute.
Phenology. Flowering and fruiting specimens of the new species were collected in September.
Etymology. The specific epithet refers to the similarity between the new species and Isotrema hei in the morphology of lamina and flower. The Chinese name is given as "拟何氏关木通".  Preliminary conservation status. Isotrema pseudohei is currently only known from two populations in Xinping County, with fewer than five individuals at each site. Based on the present study, its Extent of Occurrence (EOO) is less than 100 km 2 and the known Area of Occupancy (AOO) is less than 20 km 2 . Furthermore, the habitat is being destroyed by road construction and small-scale agriculture. Besides, the root of Isotrema itself is often harvested for medicinal purposes by the locals. Although further investigation is necessary to fully map its distribution, it is considered to be Vulnerable (

Discussion
Characterized by a horseshoe-shaped perianth and a 3-lobed gynostemium with each lobe consisting of two oblong stamens, the new species is shown to be a member of Isotrema (Zhu et al. 2019a). Isotrema pseudohei is similar to I. hei in the shape of lamina (Fig. 4A & D), but differs in the morphology of flowers, the inner surface of limb is yellow with purplish red patches and throat suborbicular, yellow, and 7-9 mm in diameter in I. pseudohei ( Figure 4C), whereas the inner surface of limb yellowish green and densely covered with purple papillae and throat circular, yellowish green with purple patches, and 4-5 mm in diameter in I. hei ( Figure 4F). Though sharing similar morphology of flowers (Fig. 4B, C, H, J), I. pseudohei can be easily distinguished from I. moupinense by the shape of lamina, which is lanceolate in the new species ( Figure 4A), but ovate in I. moupinense ( Figure 4G). Moreover, I. pseudohei also differs in the gynostemium lobes acute at apex ( Figures 2D & 4C), whereas round at apex in I. hei ( Figure 4F) and I. moupinense ( Figure 4I). Detailed morphological comparisons are provided in Table 1 and shown in Figure 4. Geographically, the new species is currently only known from Xinping County in central Yunnan, I. hei is restricted to Wenshan City in Southeast Yunnan, while I. moupinense is widely distributed in Southwest China ( Figure 5).