Hoya soidaoensis Kidyoo, 2013

Kidyoo, Manit, 2013, Hoya soidaoensis (Apocynaceae: Asclepiadoideae), a new species from southeastern Thailand, Phytotaxa 105 (2), pp. 45-50 : 45-49

publication ID	https://doi.org/ 10.11646/phytotaxa.105.2.3
persistent identifier	https://treatment.plazi.org/id/BE3487C4-FFD6-EA22-FF3C-F9DCE238FBC8
treatment provided by	Felipe
scientific name	Hoya soidaoensis Kidyoo
status	sp. nov.

Treatment

Hoya soidaoensis Kidyoo View in CoL , sp. nov. ( Fig. 1 View FIGURE 1 )

Species H. caudatae Hook. f. affinis , sed foliis minoribus ellipticis apice acutis basi cuneatis vel acutis margine non corrugatis, corpusculo oblongo-lanceolato differt.

Type:— THAILAND. Chanthaburi: Khao Soi Dao Wildlife Sanctuary , 1400 m, 5 September 2010, M. Kidyoo 1526 (holotype BCU!, isotype BKF!) .

A small climbing epiphyte. Stem and branches cylindrical, 2–3 mm in diam., greenish brown to reddish brown, pubescent, internodes 1–5 cm long, with well-developed adventitious roots. Leaves: petiole pubescent, 3–6 mm long, 1.2–1.8 mm diam.; blade thick coriaceous, elliptic, 2–3.5 × 0.9–2.2 cm, margins entire, not revolute but occasionally faintly recurved; adaxial surface green, rough with scattered hairs; abaxial surface pale green with scattered hairs on margin; apex acute, base cuneate to acute; midrib and nerves inconspicuous on both sides, lateral veins 4–5 pairs, acute angles to the midrib. Inflorescences extra-axiliary, slightly concave in top view, positively geotropic, 5–12–flowered; flower buds pentagonal shaped with reddish brown acuminate apex, lobes greenish yellow; peduncle slender, perennial, 2.7–6.6 cm long, 1.2–1.7 mm diam., pubescent. Pedicels of the peripheral flowers 1.4–2.4 cm long, and 0.9–1.1 cm for those towards the center, pinkish or greenish white with scattered reddish purple spots, pubescent, various length. Calyx greenish to reddish brown, lobes 5, nearly divided, ovate, 1.2–1.6 × 0.9–1.1 mm, apex acute, abaxial surface sparsely pubescent, inside with a small basal gland between lobes. Corolla rotate, creamy to yellowish white, ca. 1.3– 1.5 mm diam., adaxial surface densely pubescent with densely long straight hair along the margin of the lobes, abaxial surface glabrous, the connated part 2.7–3.0 mm long; lobes reflexed, revolute, ovate, 0.8–0.9 × 0.4– 0.5 mm, apex acuminate. Corona creamy to pinkish white, 6.7–6.9 mm in diam., coronal scales oblong, 2.7– 3.1 × 1.3–1.5 mm, upper surface convex, lower surface sulcate, outer angle slightly upcurved with rounded apex; inner angle raised up higher than outer angle, lateral side with membranous edge, apiculus of inner angle acute with pale pink to red color; anther appendages lanceolate, white, 1.7–2.0 mm long, erect, covering the stigma head. Pollinarium: pollinia obliquely oblong, yellow, 0.81–0.83 × 0.27–0.29 mm, apex truncate, margins pellucid extending over the dorsal margins of the pollinia; caudicles stout, hyaline, with broad wing, yellow, 0.68–0.70 × 0.27–0.28 mm; corpusculum reddish brown, oblong-lanceolate, 0.62–0.64 × 0.17–0.19 mm. Pistil: 2-ovaries, glabrous, ca. 2 mm long; stigma head conical, subquadrangular. Follicles linearlanceolate in outline, pale green with scattered reddish brown spots, 8.0 cm long, 0.4 cm diam.

Distribution:— Thailand (Chanthaburi Province).

Habitat & Ecology: —The species grows on tree trunks and branches, and occurs in both semi-exposed and shady areas in hill evergreen forest at 1400 m elevation. Flowering in July–September.

Observations:— Hoya soidaoensis is related to H. caudata and H. flagellata ( Table 1, Fig. 2 View FIGURE 2 ). It is worth noting that Kerr (1940) described H. caudata and H. flagellata as two distinct species, but they were subsequently considered to be conspecific by Rintz (1978). After detailed investigations, it was now found that these two taxa are obviously dissimilar in characters of leaves, corona scales and anther appendages ( Table 1; Fig. 2 View FIGURE 2 ). Therefore, H. flagellata should be accepted as a distinct species, and the morphological characters of the specimens of H. soidaoensis collected in this study were compared with those of both H. caudata and H. flagellata .

Morphologically, H. soidaoensis is most similar to H. caudata . Both species have positively geotropic, extra-axillary cymes with slender perennial peduncles. Their corolla is rotate with ovate lobes and acuminate apex. The margin of the lobes is densely covered with long straight hyaline hairs on the adaxial surface. Their anther appendages are lanceolate, about 2–3 mm long. Their pollinaria comprise winged caudicles ( Table 1; Fig. 2 View FIGURE 2 ). On the other hand, H. flagellata has somewhat more distinctive features. The apex of its corolla lobes is long-caudate and the anther appendages are linear. These characters are clearly different from those of H. soidaoensis and H. caudata .

Despite sharing some characters, H. soidaoensis and H. caudata posses many diagnostic features that separate one species from the other. Hoya soidaoensis obviously differs from H. caudata in leaf characters ( Fig. 2 View FIGURE 2 ). It has small elliptic leaves with cuneate to acute base and acute apex. Its leaves are light green without white blotches on the adaxial surface. The leaf margins are entire and not revolute. On the other hand, H. caudata possesses larger ovate leaves with rounded to cordate base and acuminate apex. The color of leaves is dark green with white blotches all over the adaxial surface of the blade. Its leaf margins are strongly wrinkled and revolute.

Considering the pollinarium structure ( Fig. 2 View FIGURE 2 ), the pollinaria of H. soidaoensis are clearly different from those of the two related taxa. Hoya caudata and H. flagellata have ovate corpuscula extending for less than half the pollinia length, whereas H. soidaoensis has larger pollinia and its corpusculum is oblong-lanceolate and nearly as long as the pollinia length.

Regarding the geographical distribution, H. caudata commonly occurs in the Malay Peninsula, Singapore, Sumatra, and Borneo ( Hooker 1883, Rodda & Ang 2012), and has not been reported in natural habitats in Thailand, while H. flagellata and H. soidaoensis occur in southern and southeastern Thailand, respectively. Furthermore, all these related species occur in different habitats. Hoya soidaoensis grows in hill evergreen forest at about 1,400 m elevation. Hoya caudata is usually found in lowland forest on limestone hills ( Hooker 1883, Ridley 1923, Rintz 1978), while H. flagellata grows in lowland evergreen forest from about sea level to 500 m elevation.

Overall, the results from this study strongly suggest that there are significant discontinuities in vegetative and floral characters as well as ecology between H. soidaoensis and its two closely related species. The description of H. soidaoensis as a new species of Hoya from southeastern Thailand can thus be considered sufficiently supported. A key to H. soidaoensis and the two related taxa is presented below.

Additional specimen examined (paratype):— THAILAND. Chanthaburi: Khao Soi Dao Wildlife Sanctuary , 1400 m, 6 September 2010, M. Kidyoo 1547 ( BCU!) .

Additional specimens of the related taxa examined:

Hoya caudata : — MALAYSIA. Malacca, s. dat., A.C. Maingay 1128 (type K!) ; THAILAND. Bangkok (cultivated plant), 19 February 2009, M. Kidyoo 1393 ( BCU!) .

Hoya flagellata : — THAILAND. Satun: Tarutao , 18 January 1928, A.F.G. Kerr 14164 (type K!) ; 24 July 2010, M. Kidyoo 14 25 ( BCU!) ; Nakhon Si Thammarat: Khao Nan National Park , 22 July 2010, M. Kidyoo 1422 ( BCU!) .