Apios delavayi Franchet (1890: 180–181)

Zhang, Fan, Feng, Si, Zhou, Jianjun, Zhang, Rong, Liu, Linhan, Yang, Chengzi, Yu, Xunlin & Pan, Bo, 2018, Apios chendezhaoana (Fabaceae), an overlooked species and a new combination from China: evidence from morphological and molecular analyses, Phytotaxa 371 (1), pp. 1-16 : 8-9

Apios delavayi Franchet (1890: 180–181) .

Type:— CHINA. Yunnan, 14 September 1886, M. Delavay 2323, Barcode P00237786 (holotype P!).

Perennial herbs. Tuber single, fusiform, 2–5 cm in diameter, 5–20 cm long. Leaves pinnately compound, 8–32 cm, (3–) 5–9 (–11) leaflets. Leaflets highly variable, ovate to lanceolate, apex acuminate to acute. Racemes shorter or much longer than leaves. 2–30 flowers, lax. Calyx 2-lipped. Corolla light yellow, yellowish white, greenish yellow, yellowish purple, or dark purple; standard orbicular, pocket shaped, covering the tip of keel; wings shortest, reflexed; keel narrow, curved to semicircular, longer than standard. Legume linear or falcate, attenuate at base, 7–15 cm.

Apios delavayi Franchet (1890) , Apios macrantha Oliver (1890 , October: pl. 1946), Apios gracillima Dunn (1903: 488–489) , and Apios delavayi var. pteridietorum Handel-Mazzetti (1933) , are all from SW China, and distinguished by flower color, inflorescence length, leaflet width, and flower number of each inflorescence ( Sa & Gilbert 2010). However, only the name A. delavayi is frequently adopted during identification, and the other three names have seldom been used. Ren et al. (2007) considered that A. gracillima should be recognized as a distinct species, according to evidence from the leaf epidermis. However, using only microscopic evidence during taxonomic delimitations and treatments is not recommended. After examination of hundreds of specimens from CDBI, KUN, PE, and SM, we found they all have very similar flower shapes, with various colors from pale yellow, light green, greenish white to yellowish violet, light purple, and even dark purple. Leaflet numbers vary from 3 to 11; leaflet shape from linear to narrow lanceolate, lanceolate, and ovate; inflorescence longer or shorter than leaves, and flowers 6–30 or 2–4 per inflorescence. They all have the following consistent characters: lax inflorescence, broad standard, long curved circular keel, falcate pod, fusiform tuber, and a high elevation distribution between 1300–3800 m. We therefore include all the four taxa into one species, Apios delavayi , as synonyms or varieties.

Because both A. delavayi and A. macrantha were published in 1890, while A. macrantha is not widely used, here we propose to conserve A. delavayi against A. macrantha . Interestingly, populations east of the Mekong-Salween Divide always have pale yellow to greenish white flowers, while populations west of the divide have light purple to dark purple flowers. Types of Apios delavayi and A. macrantha were both collected from the east part, and present greenish white or pale yellow flowers, while the type of A. delavayi var. pteridietorum was collected from west of the divide, and bears purple flowers. The Mekong-Salween Divide is an important floristic boundary between the eastern Himalaya and Hengduan Mountains ( Luo et al. 2017), so we adopt both A. delavayi var. delavayi and A. delavayi var. pteridietorum as accepted names to represent the distinct distribution of flower colors.