The taxonomic revision of Asian Aristolochia (Aristolochiaceae) V: two new species from Yunnan, China

Abstract Aristolochia pseudoutriformis X.X.Zhu & J.S.Ma, sp. nov. and A. yangii X.X.Zhu & J.S.Ma, sp. nov., two new species from Yunnan, China, are described and illustrated here. The former is morphologically similar to A. utriformis and A. forrestiana and the latter is similar to A. cucurbitoides and A. forrestiana. According to Ma’s (1989a) classification, both new species belong to Aristolochia subgenus Siphisia on the basis of the 3-lobed gynostemium and oblong anthers that are adnate in pairs, opposite the gynostemium lobes. Meanwhile, the two new species are assessed as Vulnerable (VU D2) according to IUCN Red List criteria.


Introduction
Aristolochia L. consists of about 550 species (González 2012) and is the largest genus in Aristolochiaceae (Hwang et al. 2003). Most species are distributed in the tropics and subtropics (Ma 1989a;Wanke et al. 2006). Three subgenera: subgenus Aristolochia, subgenus Siphisia and subgenus Pararistolochia are recognised based on morphological and molecular data (Wanke et al. 2006). China has 69 species according to Zhu et al. (2018). A key to the subgenera and a useful key to Asian species of Aristolochia subgenus Siphisia are provided by Do et al. (2015a).
During five field expeditions to Hundred Flowers Ridge in Longyang District, Baoshan, western Yunnan, two unknown species of Aristolochia were collected. Careful studies of the genus were undertaken, particularly the floral characteristics of those species in the adjacent regions, as well as morphological comparisons of the two unknown species with their related species. Meanwhile, through extensive fieldwork, careful examination of numerous specimens and colour photos and consultation of related publications, we confirm that they are two new species of Aristolochia which are described and illustrated in this study. Diagnosis. Similar to Aristolochia utriformis S.M.Hwang (Hwang 1981) and A. forrestiana J.S.Ma (Ma 1989b), but differs from the former in its lamina ovate to narrowly ovate (vs. ovate-lanceolate in A. utriformis), limb cylinder, forming obtuse angle with upper tuber, inside dark red, dense processes (vs. limb ovoid, straight extended from upper tube, inside black purple, sparse processes in A. utriformis) and throat ca. 6 mm in diam. (vs. ca. 1 mm in diam. in A. utriformis) and differs from the latter in its flower light yellow (vs. light brown or purple in A. forrestiana), limb slightly asymmetric, 2-3 × 1-1.7 cm; 3-lobed, lobes triangle or wide triangle; inside dark red (vs. asymmetric, 6-8 × 1.5-2 cm; 3-lobed, lobes lanceolate; inside black purple in A. forrestiana), as well as throat ca. 6 mm in diam. (vs. ca. 3mm in diam. in A. forrestiana). Detailed morphological comparisons are shown in Table 1 and Figure 7.
Distribution IUCN Red List Category. Aristolochia yangii is known from only three populations, with fewer than ten individuals seen at each site. Therefore, the new species is assigned a preliminary status of Vulnerable (VU D2) according to IUCN Red List Criteria (IUCN 2012), indicating a population with a very restricted area of occupancy (typically less than 20 km 2 ) or number of locations (typically five or fewer).

Discussion
Aristolochia pseudoutriformis is morphologically similar to A. utriformis (Figs. 7D-F) in the shape and colour of flower, but they can be distinguished by the morphology of lamina and limb and the size of throat. It is also similar to A. forrestiana (Figs. 7G-I) in the morphology of lamina, whereas they differ in the shape and colour of flower, the morphology of limb, as well as the size of throat (see Table 1 and Fig. 7) Aristolochia yangii is similar to A. cucurbitoides in the shape of lamina, but they can be distinguished by the morphology of flower. It is also similar to A. forrestiana (Figs. 7G-I) in the size of flower, whereas they differ in the shape and colour of flower, the morphology of limb, as well as the shape of lamina (summarised in Table 2 and comparison of A. pseudoutriformis and A. forrestiana is also shown in Fig. 7).
Both two new species with horseshoe-shaped perianth, the 3-lobed gynostemium and each lobe consisting of one pair oblong stamens belongs to Aristolochia subgenus Siphisia (Ma 1989a). These new discoveries, along with many new species recently described from China and neighbouring countries (Phuphathanaphong 2006;Liu and Deng 2009;Xu et al. 2011;Yao 2012;Huang et al. 2013Huang et al. , 2015Wu et al. 2013;Do et al. 2014Do et al. , 2015aDo et al. , 2015bDo et al. , 2015cDo et al. , 2015dDo et al. , 2017Huong et al. 2014;Lu and Wang 2014;Ohi-Toma et al. 2014;Ravikumar et al. 2014;Zhu et al. 2015Zhu et al. , 2016Zhu et al. , 2017aZhu et al. , 2017bZhu et al. , 2018Gong et al. 2018;Yang et al. 2018) provide evidence that the genus Aristolochia and especially Aristolochia subgenus Siphisia is very diverse in South-East Asia. We predict that more new species of Aristolochia will be found after extensive investigations in this region.