Hoya batutikarensis R. Ahmad, S. Rahayu & Rodda, 2021

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 : 81-84

Hoya batutikarensis R. Ahmad, S. Rahayu & Rodda , sp. nov. ( Figs. 2. 3 )

Type: — INDONESIA. Sulawesi, Central Sulawesi, Luwuk, Air Terjun Batu Tikar Luwuk , 00°56’04.48”S, 122°47’26.00”E, 9 February 2019, R. P. P . Ahmad RPPA 015 (holotype CEB!, isotype BO, SING!) .

Diagnosis:— Among the Hoya species occurring in Sulawesi, this new species is most similar to H. camphorifolia Warburg (in Perkins 1904: 129) in being an epiphytic climber, with elliptic-lanceolate leaf blades, actinodromous venation, and rotate corolla, from which it can be distinguished by the flat to slightly convex inflorescence in outline in H. batutikarensis (vs. globose in H. camphorifolia ) and the corona basal spreading process and an apical triangular process (vs. corona with simple navicular lobes in H. camphorifolia ).

Epiphytic climber with white latex in all vegetative parts. Roots adventitious, produced all along the stems. Leafy stems terete, slender, up to 5 mm in diam., creeping on the host tree trunk or pendulous, glabrous, green or pale brown; internodes 8 – 12.5 cm long. Leaves: petioles terete, fleshy, 1.5 – 2 cm long, 3–5 mm in diam., pale green, glabrous; blades elliptic-lanceolate, 8 – 17 × 3.5 – 6 cm, coriaceous, stiff, apex and base acute, pale green above, paler below, venation actinodromous, with 1 prominent basal secondary vein on each side of the midrib and 2–4 further shorter secondary veins on each side of main vein, veins paler then lamina. Inflorescence umbelliform, flat to slightly convex, 3–4 cm in diam., 3–8 flowered; peduncle extra-axillary, positively geotropic or laterally held, terete, 0.5 – 1 cm long, ca. 1.5 mm in diam., pale brown, glabrous; pedicels filiform, 0.8–1.5 cm long, white flushed pink, glabrous. Calyx lobes deltoid, ca. 2 × ca. 1 mm, apex acute, pink, glabrous; basal internal colleters lanceolate. Corolla rotate 8 – 10 mm in diam.; tube 1.5–2.5 mm long, white tinged pink, densely papillose inside, glabrous outside; lobes broadly triangular, 0.35–4.5 × 0.25–0.30 mm, apex acute, white tinged pink, densely papillose inside, glabrous outside. Gynostegium sessile; corona staminal, ca. 1 mm tall, ca. 3.5 mm in diam., flesh, purple-red; corona lobes with a basal spreading process, almost round, 1.5–2 × 1 – 1.5 mm, with revolute margins beneath and apiculate outer tips, and apical process triangular, with rounded outer angles and acuminate inner tip. Pollinia oblong, 250–270 × 110–130 µm, with truncate apex and attenuate base and evident pellucid margin; caudicles ca. 50 µm long, attached towards the middle of the corpusculum, corpusculum elliptic, ca. 100 × 80 μm. Ovaries ovoid, ca. 0.5 × 0.5 mm, glabrous. Fruit and seeds not seen.

Etymology: —The specific epithet refers to the collection locality of the type material, Batu Tikar in Central Sulawesi.

Distribution: —Endemic to Sulawesi, Indonesia, where it is found in Luwuk, Air Terjun Batu Tikar Luwuk, Central Sulawesi; Latimojong and Malili-Luwu, South Sulawesi and Kolaka, South East Sulawesi.

Habitat and Ecology: —This species was observed growing dangling from a tree along the tourist paths to Batu Tikar waterfalls, at ca. 400 m altitude. At Enrekang, South Sulawesi, this species was observed to be rooted in ant nests (S. Rahayu, pers. obs.), as also observed in other species in Sulawesi ( Kleijn & van Donkelaar 2001). The relationship between Hoya species and ants is an important ecological adaptation and an aid to seed dispersal, especially for short distance, while long distance seed dispersal is by wind ( Rahayu et al. 2010).

Provisional conservation assessment:—Endangered (EN, B2(a), b(iii); IUCN 2012).This species is known from only four localities, and its area of occupancy (AOO) is of ca. 16 km 2. One of the localities is near Batu Tikar Waterfall which is one of the leading tourist attractions in the Luwuk area, and therefore is prone to habitat degradation.

Notes: —The majority of Hoya species have a corona with simple, ovate, spreading lobes; however corona lobes can have innumerable modifications such as bearing bilobed apices, such as in species in section Acanthostemma , or erect, not spreading lobes as in H. multiflora Blume (1826: 1064) . Hoya batutikarensis R. Ahmad, S. Rahayu & Rodda is unusual because its corona lobes are formed by two discrete parts, a basal spreading process and an apical triangular process. In Sulawesi, the only other species with a somewhat similar corona morphology is H. surisana Rodda & Rahayu (2020: 212) , which however has large campanulate flowers and calyx lobes exceeding the corolla lobe sinuses. As mentioned in the diagnosis H. batutikarensis is similar to H. camphorifolia in foliage and type of corolla but distinguished by the inflorescence shape and corona morphology. Additionally, the peduncles of H. batutikarensis are 0.5 – 1 cm long, while H. camphorifolia generally has peduncles longer than 1 cm.

Additional specimens examined: — INDONESIA. Central Sulawesi, Kulawi-Resort Gimpu, 400 m, 2002, Saripudin 24 ( HBBO) ; South Sulawesi, Enrekang, Baraka, Tiktok-Kadingeh, 500 m, 29 June 2002, S . Rahayu 234 ( HBBO); South East Sulawesi, Kolaka, Latambaga, Ulunggoloka, TWA Mangolo, 120 m, April 2002, I. P . Astuti 308 ( HBBO) .

Figures

FIGURE 2. Hoya batutikarensis. A, flower, side view; B, corolla, from above; C, corona, from below; D, pollinarium. Drawing by Loh Xiang Yun, based on R.P.P. Ahmad RPPA 015.

FIGURE 3. Hoya batutikarensis. A, habit; B, inflorescence from above; C, inflorescence, side view. Based on habitat observations. Photos by W.H.Ardi.