Hoya ischnopus Schlechter (1913: 111)

Ahmad, Roland Putra Pribadi, Rahayu, Sri & Rodda, Michele, 2021, One new species and a new record of Hoya (Apocynaceae, Asclepiadoideae) from Sulawesi, Indonesia, Phytotaxa 502 (1), pp. 79-85 : 80-81

Hoya ischnopus Schlechter (1913: 111) ( Fig. 1 )

Replaced synonym: Dischidia hellwigii Warburg (1893: 205) .

Blocking name: Hoya hellwigiana Warburg (in Schlechter & Warburg 1907: 341).

Type: — PAPUA NEW GUINEA “Finschhafen, am seestrande bei kedam aud bäumen”, 1 March 1889, F. C. Hellwig 384 (holotype B, destroyed) ; PAPUA NEW GUINEA: Eitape. 12 August 1909, R. Schlechter 19965 (neotype B [ B 10 0271808], designated here) .

Epiphytic climber with white latex in all vegetative parts. Leafy stems terete, slender, up to 4 mm in diam., creeping on the host tree trunk, green or brown, glabrous; internodes 7 – 30 cm long. Leaves: petiole terete, fleshy 1.5 – 2.5 cm long, 2–3 mm in diam., pale green, glabrous; blades elliptic-lanceolate, 12 – 17.6 × 3.7 – 6 cm, apex acuminate, base obtuse, coriaceous, stiff, pale green above, paler below, venation pinnate with 3–7 secondary veins on each side of main vein, very faintly visible. Inflorescence umbelliform, globose, 3.5–5 cm in diam., 10–22-flowered; peduncle extraaxillary, positively geotropic, terete, 7 – 9 cm in diam., pale green with darker spots, glabrous. Flowers remaining open for about a week; pedicels filiform, 2–2.4 cm long, cream-coloured with darker dots, glabrous. Calyx lobes deltoid, 0.6–0.7 × ca. 0.5 cm, acute at apex, green or cream-coloured, glabrous; basal colleters lanceolate. Corolla rotate, 1.7 – 1.9 cm in diam.; tube 3–4 mm long, cream-coloured, tinged greenish, sparsely pubescent inside, more densely pubescent towards the distal portion, glabrous outside; lobes broadly triangular, cream-coloured tinged greenish inside, pubescent, with glabrous tip, glabrous outside. Gynostegium sessile. Corona staminal, 2.5–4 mm tall, 11–13 mm in diam., fleshy; corona lobes ovate, slightly convex above, with revolute margins beneath 3.5 – 4.5 × ca. 2 mm, greenish cream or pale pink, inner process acuminate, slightly raised, outer apex acute. Pollinia oblong, round at base, truncate at apex, with evident pellucid margin, 0.8–1.2 mm long, 0.5–0.8 mm wide; caudicles attached towards the middle of the corpusculum; corpusculum 0.5–0.6 × 0.2–0.3 mm. Ovary ovoid, 2–3 × 3–4 mm. Fruit and seeds not seen.

Distribution: —New Guinea, where it is one of the most widespread and common species on the main island, inhabiting a wide range of environments from the coast up to 1400 m altitude, both in primary and secondary forests and often even on roadside trees in towns or along the coast. In Sulawesi it is found in Tinombala, Toli Toli, Gimpu, and Morowali, in Central Sulawesi, and Aralle, Mamasa, West Sulawesi.

Habitat and ecology in Sulawesi: —Epiphyte, found in primary and secondary forest at 10–500 m altitude. In Aralle, Mamasa (West Sulawesi) several sub populations were observed in September 2019 growing in primary and secondary forests together with Hoya incurvula Schlechter (1916: 14) , H. pallilimba Kleijn & van Donkelaar (2001: 479) , and H. sulawesiana S. Rahayu & Rodda (in Rodda & Rahayu 2020: 210). In Gimpu, Central Sulawesi, a single population was observed, hanging from a tree adjacent to a river; in Morowali, two subpopulations were observed, climbing on trees; the Toli Toli collection was made in degraded secondary forest.

Provisional conservation assessment:—Least Concearn (LC; IUCN 2012). Hoya ischnopus is a very widespread species and it is very common in its main distribution area in New Guinea.

Notes: —The discovery of Hoya ischnopus in Sulawesi, far away from its known distribution area in New Guinea may appear to be highly unusual. However, it is not uncommon to greatly extend the known distribution areas for Hoya species. For instance, H. australis Traill (1830: 28) , a species formerly known from Australia, Papuasia and Melanesia ( Forster & Liddle 1991; Liddle & Forster 2008) was also collected in Sulawesi and Borneo (Lamb & Rodda 2017), and H. erythrina Rintz (1978: 501) , a species formerly considered endemic to Peninsular Malaysia was also collected in Thailand and Vietnam. ( Averyanov et al. 2017). Hoya ischnopus is quite variable in leaf shape (lanceolate to oblong), base (acute to round or subcordate) and margins (entire to undulate). The flowers are borne on globose to convex inflorescences, and the rotate flowers are generally cream-yellow-orange, but can also sometimes have pink, green and red flushes.Among Sulawesi species, H. ischnopus is most similar to H. dolichosparte Schlechter (1916: 13) and H. obovata Decaisne (1844: 635) as the three species have globose or convex inflorescences, and rotate, pubescent corollas. The three species can be separated based on leaves, which are broadly elliptic and with actinodromous venation in H. dolichosparte , broadly elliptic to round in H. obovata with almost indistinct venation, while the leaf blades are elliptic-lanceolate and with pterodromous venation in H. ischnopus .

Original material (Hellwig 384) of Dischidia hellwigii Warburg (1893: 205) could not be traced at B, BO or L, where Hellwig materials were deposited (Van Steenis-Kruseman 1950). Therefore, we designate Schlechter 19965 at B as neotype of this name, which is one of the specimens cited by Schlechter when he published Hoya ischnopus .

Additional specimens examined:— INDONESIA. Central Sulawesi, Parigi-Montog, Tinombala , c. 500 m., August 2002, R . Sari 85 ( HBBO); Gimpu , 01°36.877” N, 120°03.757” E , 495 m, 26 August 2019, R. P. P . Ahmad RPPA020 ( CEB); Morowali , 02°07.324” N, 121°10.627” E , 132–199 m, 4 May 2020, R. P. P . Ahmad RPPA033 ; Toli Toli, Air Terjun Malangga , 01°07’56.76”N, 120°53’50.30”E, 18 January 2019, Zulfadli ZF 37 ( BO, CEB, SING) ; West Sulawesi, Mamasa, Aralle, ca. 500 m, Andarias s.n., vouchered in cultivation at Bogor Botanic Garden, 30 September 2019, S . Rahayu 1232 ( BO) .

Figures

FIGURE 1. Hoya ischnopus. A, habit (in habitat in Toli Toli, 18 January 2019); B, E, flower from above; C, F, flower from below; D, G, pollinarium. Based on habitat observations and microscopy observations. Photos by Zulfadli and R.P.P. Ahmad.