Marsdenia yarlungzangboensis C.Liu, J.D.Ya & Y.H.Tan, 2019

Liu, Cheng, Ya, Ji-Dong, Tan, Yun-Hong, He, Hua-Jie, Dong, Gui-Jun & Li, De-Zhu, 2019, Marsdenia yarlungzangboensis (Apocynaceae, Asclepiadoideae), a new species from Xizang, China, PhytoKeys 130, pp. 85-92 : 86-89

Marsdenia yarlungzangboensis C.Liu, J.D.Ya & Y.H.Tan sp. nov. Figs 1 , 2

Diagnosis.

Marsdenia yarlungzangboensis is morphologically similar to M. medogensis , M. tenii and M. yuei , but differs from M. medogensis in inflorescences pubescent; sepals suborbicular; corolla yellow, throat red and densely pilose, shorter lobes and reddish outside, apex emarginate, margin reddish and ciliate; corona lobes triangular, to base of anthers; stigma head hemispherical; and differs from M. tenii in leaf blades elliptic; sepals suborbicular; corolla yellow, throat red, lobes reddish outside, margin reddish; stigma head hemispherical, conspicuously exserted from anther appendages and corolla tube; and also differs from M. yuei in leaf blades elliptic; inflorescences unbranched and pubescent; sepals suborbicular; corolla yellow, throat red and densely pilose; lobes ovate, apex emarginate; corona lobes to base of anthers.

Type.

CHINA. Xizang: Motuo County, Renqinbeng, on margins of the subtropical evergreen broad-leaved forest, 29°20'08.59"N, 95°21'38.42"E, 1848 m a.s.l., 15 Nov 2016, in flowering, C. Liu, J.D. Ya, H.J. He & C.H. Li 16CS11914 (holotype: KUN!, isotype: KUN!)

Description.

Lianas woody, up to 10 m. Stems pale gray, sap white. Branchlets glabrous or distal parts minutely puberulent. Leaves opposite, petiole 1.5-2.5 cm, puberulent; blades elliptic, 7-12 × 3.5-6 cm, papery, glabrescent or sparsely hairy and denser along veins adaxially, base rounded or shallowly cordate, apex acuminate, margin entire, revolute, abaxially pale; lateral veins 4 or 5 pairs. Inflorescences umbel-like or with several umbel-like cymules along unbranched rachis, 3-7 cm, rachis at least 1.5 cm; peduncle 1.5-6 cm, pubescent; pedicel 5-7 mm, pubescent. Sepals suborbicular, pubescent outside, ca. 4 × 3-4 mm, ciliate, basal glands 5. Corolla yellow, campanulate, 1-1.5 cm in diam., glabrous outside, pubescent inside; tube ca. 5 mm, glabrous outside; throat red and densely pilose; lobes ovate and reddish outside, twisted to the right, 5-6 × 3-4 mm, apex emarginate, margin reddish and ciliate. Corona lobes triangular, fleshy, to base of anthers, almost flat. Anther appendages oblong, apex membranous; Pollinia 2 per pollinarium, erect, reniform. Ovary glabrous, ca. 2 mm, 2-carpelled, free. Stigma head hemispherical, conspicuously exserted from anther appendages and corolla tube. Follicles and seeds not seen.

Phenology.

Flowering from November to December.

Distribution and habitat.

Marsdenia yarlungzangboensis grows at the margins of subtropical evergreen broad-leaved forest with main community types of Castanopsis echinocarpa J. D. Hooker & Thomson ex Miquel and Quercus gambleana A. Camus, Renqinbeng, Motuo County, Xizang, China, at an elevation of 1800-2100 m.

Etymology.

The specific epithet ' yarlungzangboensis ' is derived from the type locality, Yarlung Zangbo Grand Canyon, Motuo County, southeast Xizang, China.

Vernacular name.

Yǎ Lǔ Zàng Bù Niú Nǎi Cài (Chinese pronunciation); 雅鲁藏布牛奶菜 (Chinese name).

Discussion.

Based on the larger gynandrium, corolla tube almost equal in length to gynostegium and with umbel-like cymules along unbranched rachis, Marsdenia yarlungzangboensis belongs to Marsdenia sect. Ruehssia (Karst.) Fourn. ( Tsiang and Li 1977). Morphologically, it is similar to M. medogensis , M. tenii and M. yuei in terms of habit and floral morphology, but can be distinguished from M. medogensis in inflorescences pubescent (vs. glabrous); sepals suborbicular (vs. ovate); corolla yellow (vs. white), throat red and pilose (vs. glabrous), apex emarginate (vs. rounded), margin reddish and ciliate; corona lobes triangular (vs. oblong), to base of anthers (vs. as long as anther appendages); stigma head hemispherical (vs. discoid, convex). It also differs from M. tenii in its stems glabrous or distal parts minutely puberulent (vs. densely yellow-brown tomentose); leaf blades elliptic (vs. oblong-ovate); sepals suborbicular (vs. elliptic); corolla yellow, throat red and pilose, lobes reddish outside (vs. yellowish white, throat pilose with retrorse hairs); stigma head hemispherical (vs. 2-cleft, conical), conspicuously exserted from anther appendages and corolla tube (vs. equalling anther appendages). Beyond that, it can be distinguished from M. yuei in leaf blades elliptic (vs. ovate); inflorescences unbranched, pubescent (vs. branched, glabrous); sepals suborbicular (vs. rounded); corolla yellow (vs. white), throat red and densely pilose (vs. glabrous); lobes ovate, apex emarginated (vs. oblong-obovate, apex rounded); corona lobes to base of anthers (vs. as long as anther appendages). The detailed characters amongst the three related species are provided in Table 1 .

According to field surveys, this new species is only found in the type locality Renqinbeng, Motuo County, Xizang. This area is one of China’s biodiversity hotspots and consists of a diverse series of ecosystems from subtropical broad-leaved forests to alpine meadows above the tree line with an altitudinal range of 150-6000 m above sea level. Plant diversity is also poorly studied in this area, and some new taxa have been discovered in recent years. In order to better understand and conserve the biodiversity in this area, more extensive investigations are needed in the future.

A diagnostic key to the new species and its closely related species in China

Figures

Figure 1. Marsdenia yarlungzangboensis C. Liu, J. D. Ya & Y. H. Tan A habit B flower (lateral view) C opened calyx D opened corolla E gynostegium and staminal corona F pistil G pollinarium.

Figure 2. Marsdenia yarlungzangboensis C. Liu, J. D. Ya & Y. H. Tan A habit B inflorescences and adaxial leaf surface C abaxial leaf surface D flower (lateral view) E flower (front view, showing hairy throat) F opened corolla G opened calyx H gynostegium and staminal corona I pistil J pollinarium. Photo credit: Cheng Liu (A-E) and Lian-Yi Li (F-J).