Hoya longlingensis and H. sichuanensis (Apocynaceae), Two New Species from Southwestern China †

: Hoya longlingensis (E.F. Huang) and H. sichuanensis E.F. Huang are two new species of Apocynaceae from Southwestern China that are described in this study. Morphologically, the two species resemble H. tamdaoensis Rodda & T.B. Tran and H. lyi H. L é v., respectively. However, H. longlingensis differs from H. tamdaoensis by its elliptic leaves, mid-vein of leaf blades raised adaxially and depressed abaxially, lateral veins 2–4-paired, corolla yellow-green, outer angles of corona convex and spreading outside obviously. While H. sichuanensis differs from H. lyi by its obovate leaves, leaf apex rounded and base cuneate, petioles 1–3.5 cm long and ca. 3 mm in diameter, calyx lobes triangular, and corona whitish.


Introduction
Hoya R. Br. is a large genus in the tribe Marsdenieae, subfamily Asclepiodoideae of Apocynaceae [1], with more than 300 species distributed from China and Southeast Asia to Oceania [1,2], and 32 species were recorded in Flora of China [2]. In the past decade, multiple new species or newly recorded species of this genus have been discovered in Southwestern China resulting from extensive field investigations conducted [3][4][5][6][7][8][9][10][11]. Many new species of this genus were reported from the adjacent areas of China [12][13][14][15][16][17][18][19][20]. We collected two unidentified Chinese Hoya species in Sichuan and Yunnan provinces during our recent expeditions in 2018 and 2021. After detailed morphological comparisons among congeneric species recorded from China and adjacent areas, it was concluded that the two species were new to science, thus they were formally described below.

Materials and Methods
In addition to the field work conducted in China, the present study also included investigations of Hoya material from herbaria CDBI, E, IBSC, KUN, P. and PE. Herbarium abbreviations cited here follow the Index Herbariorum [21]. Morphological characters of leaves, inflorescences, and flowers of relevant Hoya species were photographed and measured (Figures 1-3).

Taxonomic Treatments
Hoya longlingensis E.F. Huang   Diagnosis: The species is morphologically similar to Hoya tamdaoensis Rodda & T.B. Tran, but differs by its elliptic-shaped leaves, mid-vein of leaf blades raised adaxially and depressed abaxially, lateral veins of leaf blades 2-4-paired, corolla yellow-green, outer angles of corona convex and spreading outward obviously.
Distribution and Habit. Hoya longlingensis is known only from its type locality, Longling Hsien, Yunnan Province, China ( Figure 4). It is an epiphytic liana that occurs in broad-leaved evergreen forests at an elevation of 2136 m. It is usually epiphytic on stems of the Fagaceae species at a height of over 10 m.  (Figure 4). It is an epiphytic liana that occurs in broad-leaved evergreen forests at an elevation of 2136 m. It is usually epiphytic on stems of the Fagaceae species at a height of over 10 m. Etymology. Hoya longlingensis is named after its type locality, found in Longling Hsien in the Yunnan Province, China.
Taxonomic discussion. Hoya longlingensis E.F. Haung is morphologically similar to H. tamdaoensis Rodda & T.B. Tran, a species reported recently from Vietnam [18]. Both H. longlingensis and H. tamdaoensis exhibit leaves wine-red when young, leaf apex usually caudate, petioles recurved, peduncle up to 10 cm long, corolla rotate and flat, ca. 2 cm in diameter, densely pubescent adaxially and glabrous abaxially, and margin recurved. However, H. longlingensis is an epiphytic liana and twining usually on the stems of other trees ( Figure 1A), in contrast H. tamdaoensis is a lithophytic climber [18]. Additionally, H. longlingensis can be distinguished from H. tamdaoensis further by its lamina elliptic (Fig-Figure 4. Distribution of Hoya longlingensis (blue square) and H. sichuanensis (red circular).
Etymology. Hoya longlingensis is named after its type locality, found in Longling Hsien in the Yunnan Province, China.
Distribution and habit. Hoya sichuanensis is known from multiple wild populations in the Rainy Zone of West China, which is located along the west brim of the Sichuan Basin, in Sichuan Province, China (Figure 4). It can be found usually climbing on the slopes or cliffs near roadsides, at the elevation of 600-1000 m.
Etymology. Hoya sichuanensis is named after its type locality, Sichuan Province, China. Taxonomic discussion. Hoya sichuanensis is morphologically similar to H. lyi Levl., a species widely distributed in China, Laos, and Vietnam [22]. Both H. sichuanensis and H. lyi exhibit the following traits: rooting stems, many-flowered axillary pseudumbels, corolla rotate, usually white in color, densely pubescent adaxially and glabrous abaxially, margin recurved, corona broadly ovate in top view, outer angle sub-truncate to broadly rounded, inner end acuminate. However, H. sichuanensis can be distinguished from the latter in having lamina usually obovate in shape (Figure 2A-C) (vs. oval to elliptic or oblong; Figure 3A,B), apex rounded and base cuneate or rarely rounded (Figure 2A-C) (vs. an apex that is usually acute and a base that is rounded; Figure 3A,B), petioles 1-3.5 cm long and approximately 3 mm in diameter ( Figure 2C) (vs. 3-10 mm long and 1-1.5 mm in diameter; Figure 3A), calyx lobes triangular and approximately 1.6 mm wide at the base ( Figure 2G-I) (vs. narrowly triangular; Figure 3E), corona white in color ( Figure 2B,D-F,J) (vs. ivory white with a purple centre; Figure 3D,F,G).
A key to the Hoya species mentioned above: