The species of Hoya R. Br. are generally climbers with a few species being epiphytic danglers, which do not have twining stems or adventitious roots^[1-2]. There are about 11 dangler species of Hoya mainly distributed in eastern India, Nepal, Bangladesh, Bhutan, Myanmar, northern Thailand and southwest China^[3-10]. These species, informally defined as H. lanceolata complex^[9], have some characters in common, such as pendulous stems, small leaves closely set along the stems, flat or concave inflorescence with annual deciduous peduncles, flowers with white corollas and translucent purple or yellow coronas, and so on^[9].

In a field trip to Yingjiang County, Yunnan Province near the border of China and Myanmar, a special dangler species of Hoya with small ovate leaves and terminal umbel-like inflorescences was found by the first author. The general characters of this species fit well within the circumscription of the H. lanceolata complex. After referring to the related floras and literature^[3-12], and carefully examining the herbarium specimens or photos of type specimens, we finally drew the conclusion that this unknown species is new to the science, which is described and illu- strated below.

Hoya tetrantha J. F. Zhang, Y. H. Tong & N. H. Xia, sp. nov. (Fig. 1)

(Fig. 1)

Fig. 1 Hoya tetrantha J. F. Zhang, Y. H. Tong & N. H. Xia. A: Flowering branches; B: Inflorescence, top view; C: Inflorescence, back view; D: Infructescences; E: Leaves; F: Flower, abaxial (left) and adaxial (rightmost) view; G: Corona, adaxial (up) and abaxial (below) view; H: Calyx and ovary, abaxial (left) and adaxial (right) view; I: Pollinaria, abaxial (left) and adaxial (right) view.

This new species is similar to H. dickasoniana P. T. Li, but is distinguished from the latter by having ovate to broadly ovate leaf blade with an acute and mucronate apex, four-flowered inflorescence and linear sepals.

Type: China, Yunnan, Yingjiang County, Lianhua- shan Xiang, in forests, epiphytic on trees, alt. 1 148 m, 22 April 2017, C. H. Chen & J. F. Zhang SCBG- 20170340 (holotype IBSC!, isotype KUN!).

Epiphytic shrubs with milky-white sap in all vege- tative parts. Stems much branched, sturdy, hirsute, 50- 80 cm long, 3-6 mm in diam.; internodes 5-20 mm long, dark green to nut brown; adventitious roots rare. Leaves opposite, seldom whorled of 3; leaf blade fleshy, ovate to broadly ovate, 8-25 mm×4-10 mm, widest at base, base subrounded or rounded, apex acute and mucronate, adaxially green, slightly convex, glabrous or more or less pubescent, basal colleters absent, abaxially greyish green and sparsely pubescent; lateral veins inconspicuous on both sides, mid-vein and leaf margin ordinarily with purple spots adaxially; petiole slender, 1-3 mm×ca. 0.5 mm, cylindrical, green, pube- scent. Inflorescence terminal, umbel-like, concave, (3-) 4-flowered. Bracteoles triangular-lanceolate, 1.8- 2.2 mm long, 2.5-3.2 mm long when in fruit, pubescent, apex acute, margin ciliate. Peduncle positively geo- tropic, annual deciduous, 4-6 mm×ca. 2 mm, green, hirsute. Pedicels filiform, 1.5-1.8 cm long, light green with purple spots, hirsute. Sepals linear, 6-7 mm×0.8- 1 mm, 7-8.5 mm long when in fruit, light green with purple spots, pubescent, apex acute, margin ciliate. Corolla flattened to slightly convex, pale yellowish green, 2.1-2.3 cm in diam., tube ca. 1.2 cm diam., campanulate, pubescent adaxially; lobes ovate-triangular ca. 5 mm×6 mm, apex obtuse. Corona stellately spreading, fleshy, white with purple spots, ca. 7 mm diam., ca. 2.5 mm high; lobes ovoid, ca. 3 mm×1 mm× 1 mm, apex tinged with purple, outer angles obtuse to rounded, inner angles acute and produced into a recurved simple spine. Pollinia obliquely elongate, ca. 0.5 mm×0.2 mm, margins pellucid. Ovary bi-carpellate, conical, ca. 2 mm tall, carpel ca. 0.6 mm wide at base, light green. Follicles double, 9-10 cm×ca. 0.4 cm, linear, with purple-red spots, hirsute. Seeds linear, flattened, with a tuft of white hairs. All description details come from living material.

Phenology: The species blooms in April to May and fruits in December to January next year.

Etymology: The specific epithet refers to its four- flowered inflorescence.

Habitat and distribution: Hoya tetrantha is epiphytic on tree trunks in evergreen broad-leaved forest at altitudes of 1 100-1 200 m. It is so far only known from the type locality, i.e. Yingjiang County, Yunnan Province of China.

Additional specimen examined (paratype): China, Yunnan, ibid., 16 September 2016, C. H. Chen & J. F. Zhang SCBG-20160705 (IBSC).

Notes: There are two inflorescence types in the 11 species of H. lanceolata complex: seven species have both terminal and axillary inflorescences at the same time, such as H. lanceolata Wall. ex Don (the description of the inflorescence of this species in the protologue writes terminal, but the type specimen (Wallich 8164A) of this species obviously bears axillary inflorescences), H. bella Hook., H. paxtonii Nich., H. vaccinioides Hook. f., H. chinghungensis Gilbert et al., H. weebella Kloppenb. and H. kingdonwardii P. T. Li, while the other four species, i.e. H. dickasoniana, H. engleriana Hoss., H. linearis Wall. ex Don and H. daimenglongensis Shao Y. He & P. T. Li bear terminal inflorescences only. According to our observation, this character is very stable in the species of H. lanceolata complex, but seems to be overlooked in many previous studies^{[9, 15-16]}. For now, including our new species, a total of five Hoya species are known to only have terminal inflorescences. Among them, H. daimenglongensis, H. linearis and H. engleriana all have linear leaves, which can be easily distinguished from H. dickasoniana and this new species. Hoya dickasoniana, published by Li (1994) based on only one collection (F. Kingdon-Ward 21152), was described as having 3-6-flowered inflorescences. However, after our careful examination of the holotype, it was found that there are two terminal inflorescences with 5 and 7 flowers on the specimen, respectively. So, the accurate number of flowers in one inflorescence of H. dickasoniana should be 5-7. Hoya tetrantha is different from H. dickasoniana in its ovate or broadly ovate (vs. elliptic to ovate) leaf blade with an acute and mucronate (vs. obtuse) apex, (3-)4-flowered inflorescence (vs. 5-7) and flowers with linear (vs. oblong) sepals 6-7 mm long (vs. 2-2.5 mm). A detailed comparison between the two species was shown in Table 1.

(Table 1)

Table 1 Morphological comparison of Hoya tetrantha and H. dickasoniana Character H. tetrantha H. dickasoniana Stem length (cm) 50-80 20-35 Leaf blade shape Ovate to broadly ovate, widest at base Elliptic to ovate, widest at the middle Leaf blade apex Acute and mucronate Obtuse Leaf blade base Subrounded or rounded Broadly cuneate or rounded Number of flowers per inflorescence (3-)4 5-7 Sepal shape Linear Oblong Sepal size (mm) 6-7×0.8-1 2-2.5×ca. 1

Table 1 Morphological comparison of Hoya tetrantha and H. dickasoniana