Hoya corneri Rodda & S.Rahayu, 2018

Rodda, Michele & Rahayu, Sri, 2018, A revision of the Hoya uncinata complex (Apocynaceae, Asclepiadoideae), with description of a new species, Phytotaxa 383 (3), pp. 252-258 : 256-257

publication ID	https://doi.org/ 10.11646/phytotaxa.383.3.2
persistent identifier	https://treatment.plazi.org/id/03F187F4-FFD2-FFEB-FF04-3986FAB7FC67
treatment provided by	Felipe
scientific name	Hoya corneri Rodda & S.Rahayu
status	sp. nov.

Treatment

Hoya corneri Rodda & S.Rahayu View in CoL spec. nov. ( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Most similar to Hoya uncinata by the deeply lobed, rotate corolla, and large corpusculum; from which it can be distinguished by the corolla 0.9–1.3 cm in diam. (vs. 1.5–1.7 cm in H. uncinata ), peduncles orientation (negatively geotropic in H. uncinata , positively geotropic in H. corneri ), and outer corona process (with an incurved membranaceous appendage in H. uncinata , lacking appendage in H. corneri ).

Type:— Malaysia, Johore, Jason Bay, 13 June 1934, Corner s.n. (holotype SING [ SING 0121228])

Delicate epiphytic climber with clear latex in all vegetative parts; all vegetative parts glabrous. Leafy stems cylindrical, slender, 1.2–2.5 mm in diam., grey, with membranaceous peeling bark; internodes 5–15 cm long. Petioles terete, fleshy, 5–15 × 2–4.5 mm in diam., thicker than stems; lamina lanceolate, fleshy, (5–)7–10(–15) × 2–5 cm, apex acute-acuminate, base cuneate, pale to mid green above, turning red in bright light with numerous grey spots, darker green along midrib and secondary veins, pale green underneath, darker green along midrib and secondary veins, venation pinnate, secondary veins 5–8 each side, tertiary venation reticulate, basal colleters evident only on immature leaves, broadly triangular, c. 0. 5 × 1 mm. Inflorescences sciadioidal or globular, 3–4 cm in diam., 4–20 flowered; peduncles positively geotropic, extra-axillary, terete, 1–5(–10) cm × 1.5–2.5 mm in diam., glabrous; pedicels 10–23 mm × 0.5– 0.8 mm in diam., glabrous. Calyx lobes tringular, white-pink 1.2–2.2 × 0.7–1.2 mm, apex rounded, glabrous inside, slightly papillose outside; colleter 1 in each sepal sinus, oblong, 0.15–0.3 mm. Buds conical, apically 5-ridged, c. 3.2 × 4.5 mm. Corolla rotate, deeply lobed, 0.9–1.3 cm in diam, white tinged pink, almost completely yellow when exposed to high light levels, thinly and minutely pubescent inside, outside glabrous, tube 1–2 mm long, 3–4 mm in diam., lobes laterally recurved, narrowly rhomboid 3.5–6 × 3–4.5 mm, with a triangular acuminate apex, lobe tips inflexed. Gynostegium stalked, corona column conical 1–1.2 × c. 2 mm diam, glabrous; Corona staminal, 1.7–2.2 mm high, 4.5–6.5 mm in diam., fleshy, yellow with a purple centre; corona lobes ovate, laterally compressed, concave above, with revolute margins beneath, 2–3 mm × 0.9–1.3 mm, inner process erecto-patent, linear with an acute tip, as long as the anthers, outer process round. Anthers ovate, 1–1.2× c. 0.8 mm, with apical round membranaceous appendage as long as the style-head apex. Pollinia oblong, with obliquely truncate apex and base and evident pellucid margin, 0.35–0.45 × 0.150–0.18 mm; caudicles attached at the base of the corpusculum, oblong, c. 70 × 50 μm, corpusculum 500–550 × 200–250 μm; style-head 5-angled in cross section, with 5 spreading lobes alternating with the stamens, style-head apex globular, 1–1.2 mm diam.; ovary linear, 1.5–1.8 mm long, each carpel 0.3–0.5 mm wide at the base. Fruits and seeds not observed.

Etymology: — Hoya corneri is dedicated to the collector of the type specimen, E.J.H. Corner (1906–1996), assistant director at the Singapore Botanic Gardens from 1926 to 1946.

Notes: — Hoya corneri is part of the Hoya uncinata complex because it has clear latex, deeply lobed rotate corolla and corpusculum of the pollinarium almost as large as the pollinium. Compared to Hoya ruthiae it has flowers 0.9–1.3 cm in diam. (vs. 1.8–2.2 cm in H. ruthiae ) and corolla lobes are narrowly rhomboid (vs. narrowly lanceolate in H. ruthiae ).

Hoya corneri is instead more similar to Hoya uncinata due to their rotate corolla. The corolla of H. corneri is 0.9– 1.3 cm in diam. when flattened (vs. 1.5–1.7 cm in H. uncinata ), with lobes 3.5–6 × 3–4.5 mm. (vs 6–7(–9) × 4.4–5.5 mm in H. uncinata ). Other differences between the two species are the orientation of the peduncles that are mostly negatively geotropic in H. uncinata and positively geotropic in H. corneri and the shape of the outer corona process that is ending in an incurved membranaceous appendage in H. uncinata and is without appendage in H. corneri .

Distribution and ecology: —Borneo (Sanggau, West Kalimantan), Southern Thailand (Songkhla Province) and peninsular Malaysia (Negeri Sembilan and Johor). Hoya corneri has been observed in situ at Tone Dhad Fha waterfall, Thailand, as a vigorous climber in lowland primary forest. The plant was common near the waterfall and climbing up to 10 m high (S. Somadee, pers comm.). This species was also recently observed in peat swamp forest or riverside in West Kalimantan, Indonesia at 100–200 m (Ewaldus Henny pers comm.).

Conservation status: —At the two sites where H. corneri was recently observed (in Sanggau, West Kalimantan, and Tone Dhad Fha waterfall, Thailand) numerous specimens were seen, with about 50 plants counted in Sanggau. The species is only known from two further localities in peninsular Malaysia, the first in a forest reserve (Pasoh Forest Reserve) the second in Jason Bay, an area with some remnant natural vegetation. The estimated EOO is> 200,000 km 2 and the estimated AOO is c. 16,000 km 2. We suspect that the species might be more common than its herbarium records suggest, and we propose a preliminary IUCN assessment for Hoya corneri as Least Concern (LC, IUCN 2017).