Hoya is the largest genus of about 350-450 species of Apocynaceae^[1]. Most species diverse in tropical and subtropical South and Southeast Asia, but the distribution area of the genus extends all the way to the Himalayan foothills to the northwest, Okinawa to the northeast, Australia to the south and Fiji Islands to the southeast^[2].

The genus is represented by around 38 species and one variety in China^[3]. Most of which are distributed in southwestern China which including southern Tibet, western Sichuan Province, western Guizhou Province, Yunnan Province and Guangxi Province, the distribution area also include Southern China coastal which including Hainan Province, Guangdong Province, southern Fujian Province, Hong Kong, Macao and Taipei China^[3-6].

In July 2015, a handsome of Hoya in being non-laticiferous was collected by Mr. Mo from Malipo Xian, Yunnan Province, China, was brought to the first author for identification. It was not until March 2017 that the species blossomed in the Southern China Botanical Garden, Chinese Academy of Sciences (SCBG). It was identified as Hoya vangviengiensis Rodda & Simonsson which was represented in Vang Vieng prov., Lao PDR by 2012^{[3, 5, 7]}, new to China.

万荣球兰  新拟Fig. 1

Hoya vangviengiensis  Rodda & Simonsson, Webbia 67: 23. 2012. Holotype: Lao PDR, Vientiane prov. Vang Vieng, 26 Apr. 2010, Tang, Rodda & Simonsson, LT10-076 (SING, photo!).

Epiphytic vine, non-laticiferous, epiphytic or twinning on the river side of the trees or rocks. Stems pendulous or twinning, up to 10 m long, cylindrical, 2-3 mm diam., pubescent. Internodes 2-15(20) cm long. Leaves opposite, petioles cylindrical, 5-20 mm× 2-4 mm pubescent; leaf blades ovate or broadly lanceolate, 8-18 cm×3-5 cm, fleshy, becoming rather succulent when getting old, base rounded or rotund, margin slightly recurved, apex obtuse or acuminate, apex caudate with a tail 5-10 mm long, pubescent on both sides, dark green adaxially, greyish green abaxially; when fresh, midrib and lateral veins conspicuous on adaxial surface only, pinnate, secondary veins 4–5 on each side, basal ones mostly reached near the lamina margin, upper most held at an acute angle to mid vein, anastomosing along the lamina margin. Inflorescences perennial, interpetiolar, positively geotropic, umbelliform, convex, with up to 20 flowers, thick aroma; bractlets triangular, 3.5-4 mm×1.6-2 mm, pilose, margin ciliate, apex acuminate; peduncle 10-30 mm×1.5-2 mm, bearing scars of pedicle of previous year, pilose; pedicel 30-40 mm×0.8-1.2 mm, aubergine or pale green, pilose; sepals lanceolate, 6-7 mm×1-1.2 mm, acute apex, pilose, margin ciliate; corolla flat with revolute margins, white with pink spots, 20-22 mm in diam., hirsute adaxially, abaxially glabrous, margins ciliate, lobes broadly ovate, 6-8 mm×6-7 mm, apices acute; gynostegium ca. 3 mm tall; corona lobes five, adnate vertically to gynostegium, fleshy, rhomboid, almost flat, 4-5 mm×2-2.1 mm, outer process acute, with basal revolute margins; inner process apiculate, about 1 mm lower than the anther appendages; pollinaria erect, ca. 840 μm long; pollinia oblong, ca. 692 μm× 240 μm, compressed, with round apex and base, and prominent pellucid margin, corpusculum ca. 250 m× 150 μm, caudicles ca. 100 μm long; ovary bi-carpellate, broadly ovate, 1.2-1.5 mm tall, glabrous, light green. Fruits and seeds not seen. All measurements from fresh material prior to pressing.

Distribution: Lao PDR (Vientiane prov. Vang Vieng), China (Yunnan prov. Malipo County).

Habitat: Hoya vangviengiensis is only known from Malipo Xian, Wenshan Zhuang and Miao Autonomous Prefecture in Yunnan, where it epiphytic or twinning on the river side of the trees or rocks, 800 m. This species flowers from Mid-March to May.

Additional specimens examined: China. Guangzhou: SCBG, cultivated, 40 m, 15 Mar. 2017, Jing-Feng Zhang, ZJF-20170001, ZJF-20170002 (IBSC).

Notes: Most species of the genus Hoya R. Br. have coloured latex in all vegetative parts. But a small number of them is non-laticiferous (i.e. with clear sap in the foliage)^[7], e.g. H. carnosa R. Br., H. carnosa var. gushanica W. Xu, H. cordata P. T. Li & S. Z. Huang, H. fungii Hechi, H. jianfenglingensis S. Y. He & P. T. Li, H. motoskei Teijsm. & Binn., H. revolubilis Tsiang & P. T. Li and the above mentioned species of H. vangviengiensis. In addition, two species, H. commutata M. G. Gilbert & P. T. Li and H. salweenica Tsiang & P. T. Li, are morphologically similar to the above species that present clear sap, but no living plants of them are available to check whether they are also nonlaticiferous or not. All these species occur towards the northeastern limit of the distribution area of the genus, in southwestern China, coastal regions of southern China and neighboring countries. Clear sap is not only limited to those Chinese species, but 3 species in Philippines or Borneo. e.g. H. pubicalyx Merr. from Philippines, H. monetteae T. Green and H. ruthiae Rodda from Borneo^{[1-2, 7]}. Generally, most species being lack of coloured latex is recognized by rotate corolla with thickly pubescent inside and rhomboid corona lobes with narrow inner and outer corona lobe processes^[1]. But H. ruthiae is a special kind species that morphologically similar to H. uncinata Teijsm. & Binn. with coloured latex by deeply lobed rotate corollas and laterally compressed corona lobes^[1].

Hoya vangviengiensis can be easily distinguished from these species being non-laticiferous by its sepals lanceolate, longer than 5 mm.

Acknowledgments: We are grateful to the curators of the following herbaria for access to material under their care: HITBC, IBK, IBSC, KUN, A, K, PE, P, E, NY.