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.

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.

Back to history, the systematic position of these 3-lobed gynostemium species in Aristolochia has been controversial. They have successively been recognized to be different genera by different authors, i.e., Isotrema Rafinesque (1819a: 195) (Rafinesque 1819b, Huber 1960, 1985, 1993, Wu et al. 2003, 2006, 2011, Eberhard et al. 2015, Liu et al. 2015), Hocquartia Dumortier (1822: 30) or Siphisia Rafinesque (1828: 62) (Rafinesque 1836, Klotzsch 1859). On the other side, the species having 3-lobed gynostemium were also ascribed to Aristolochia subgen. Siphisia (Duchartre 1854: 29) Schmidt (1935: 236) by many researchers (Duchartre 1854, 1864, Bentham & Hooker 1880, Solereder 1889, Schmidt 1935, Hwang 1988, Ma 1989, González 1999, González & Stevenson 2000, Murata et al. 2001, Adams et al. 2005, Xu et al. 2011, Do et al. 2015a, 2015b, Wu et al. 2015, Zhu et al. 2018). Recently, Aristolochia subgen. Siphisia was re-instated as an independent genus Isotrema, which is characterized by the following set of characters: such as a strongly curved perianth with a 3-lobed limb, and especially the 3-lobed gynostemium, anthers paired on the outer surface of each gynostemium segment (Zhu et al. 2019a). It has been adopted when some new species are described (Li et al. 2019, Zhou et al. 2019, Zhu et al. 2019b, Cai et al. 2020a). Most species described under Aristolochia subgen. Siphisia have been transferred to Isotrema (Zhu et al. 2019a), but four new species published after that (Peng et al. 2019, Zhu et al. 2019c, Cai et al. 2020b) have not been transferred to Isotrema and new combinations are still necessary.

Isotrema sanyaense R.T.Li, X.X.Zhu & Z.W.Wang, sp. nov., a new species from Hainan island, China, is described and illustrated here. It is morphologically most similar to I. ledongense (Han Xu, Y.D.Li & H.J.Yang) X.X.Zhu, S.Liao & J.S.Ma and I. jianfenglingense (Han Xu, Y.D.Li & H.Q.Chen) X.X.Zhu, S.Liao & J.S.Ma in the shape of leaf, flower, and the yellow to brown villous indumentum of the pedicel, ovary and calyx. However, I. sanyaense can be easily distinguished from the latter two species by its 1-5-flowered cymes, in hanging clusters of 1 to numerous branches, upper calyx tube obviously longer than basal calyx tube, calyx limb discoid, yellow inside, with purple-red stripes and spots, about 13-18 mm in diameter, glabrous, and a throat dark red without spots, 4-6 mm wide.

Isotrema cangshanense X.X.Zhu, H.L.Zheng & J.S.Ma, a new species from western Yunnan, China, is described and illustrated here. It is similar to I. utriforme, I. forrestianum, I. cucurbitoides and I. obliquum The major differences between them are outlined and discussed. A detailed description, along with line drawings, photographs, habitat and distribution, as well as a comparison to morphologically similar species, is also provided. Meanwhile, the new taxon is assessed as Vulnerable (VU D2), according to the IUCN Red List criteria.

Aristolochia (s. l.) is widely distributed in tropical, subtropical and temperate regions of the world, with monochlamydeous and tubular flowers, gynostemia, inferior ovaries, axile placentations, pluriovulate capsules, and others as the main characters. It is the largest genus in Aristolochiaceae, which consists of about 600 species. According to Flora of China, there are 45 species in China, 33 of which are endemic. In recent years, many new species have been discovered in China, especially in Yunnan and Guangxi. Additionally, some taxa were confirmed, reinstated, republished and revised. Isotrema, previously treated as a subgenus of Aristolochia, was recently reinstated as an independent genus based on molecular and morphological evidences. This genus has strongly curved calyxes, 3-lobed gynostemia with paired anthers on the outer surface of each gynostemium segment, and basipetally dehiscent capsules. Through extensive field work, careful examination of many specimens, digital photos and related literatures, an updated checklist and identification key of Aristolochia (s. s.) and Isotrema in China are presented here. Relevant discussions and distribution for the 17 species of Aristolochia, 58 species and one subspecies of Isotrema are also provided. Among them, I. mollis and I. neolongifolia are reinstated and illustrated, the relationship among A. gentilis, A. chuandianensis and A. gracillima, and the relationship between I. kunmingense and A. bonatii are discussed, knotty taxa, such as I. ovatifolium complex, I. cucurbitoides complex, I. griffithii complex, I. versicolor complex, I. •生物编目• © 生 物多 样性 Bio div rsity Sci nce 1144 生 物 多 样 性 Biodiversity Science 第 27 卷 生 物 编 目 dabieshanensis complex and suspected species I. saccata, are also discussed.