Rigiolepis argentii Mustaqim & Ardi, 2021

Mustaqim, Wendy Achmmad & Ardi, Wisnu Handoyo, 2021, Rigiolepis argentii (Ericaceae): a new species from Sulawesi, Indonesia, Phytotaxa 521 (1), pp. 63-69 : 64-65

Rigiolepis argentii Mustaqim & Ardi , sp. nov. ( Figures 1 & 2 )

Type: — INDONESIA: Sulawesi Selatan Province, Toraja Utara Regency, trail to summit of Mount Sesean , 2°54′17.8″S, 119°52′42.28″E, 1750 m, 7 November 2018 (fl. & fr.), Ardi 341 (holotype BO, isotype CEB) .

Diagnosis: —This species is similar to Rigiolepis moultonii (Merrill 1923: 22) Smith (1935: 336) , but differs by the persistent (vs. caducous) hairs on the abaxial surfaces of the leaves, the basal marginal glands 1–2 mm distant from the petioles (vs. c. 3 mm distant), bracteoles borne on the lower half of the pedicels (vs. the middle to near the calyx), cup-shaped calyx tubes (vs. shortly campanulate), longer filaments (c. 2 mm vs. 1.2–1.5 mm), and cupular fruits (vs. globose) (see also Table 1).

Description: —Shrubs, terrestrial or epiphytic, sub-clambering, to c. 2.5 m; root-forming tuber present. Branchlets slender, c. 1.5 mm wide, with patent pubescence mixed with shorter and lax glandular hairs, glabrescent, older stages with prominent lenticels. Leaves: petiole 3–3.5 × 1.5 mm, pubescent; blades ovate-oblong, ovate-lanceolate or ellipticlanceolate, 4.8–11.8 × (1.8–) 3.2–4.1 cm, base usually rounded or nearly so, often slightly oblique with one side shallowly cordate and the other rounded, less often broadly cuneate, extreme base slightly contracted and decurrent, margin entire, slightly revolute or planar, basal gland 1 per side, impressed, at 1–2 mm distance from the petiole, apex caudate-acuminate; midvein and lateral veins impressed above; lateral veins 3–4 on each side of midvein; reticulation distinct above, distinct to ± obscure beneath; pubescent on both surfaces, glabrescent except on major veins adaxially, pubescence persistent abaxially, mixed with minute glandular hairs. Inflorescence a secund raceme, solitary or in pairs, simultaneous or sequential, (1–)9–11-flowered, rachis 1.2–4.3 cm long, with patent pubescence mixed with shorter glandular hairs; bracts ovate with long acuminate apex, 1.3–1.8 mm long; pedicels red when young, turning green, bright yellow and reddish at late fruiting stages, 5.0– 7.3 mm long, with patent pubescence mixed with shorter glandular hairs (these more prevalent than on rachis); bracteoles borne on lower half of pedicel near either base or middle, ovate-deltoid, c. 1 mm long. Flowers 5-merous. Calyx tube cup-shaped, c. 0.8 mm long, ± hairy, hairs 0.15–0.3 mm long, also with shorter glandular hairs; lobes red, deltoid, c. 1.3 mm long, sparsely pubescent outside, glabrous inside, apex acute. Corolla pale yellow, broadly urceolate, c. 4.5 × 4.5 mm, slightly 5-angled with the ribs distinct when dry, outside with scattered hairs on ribs, otherwise glabrous, inside glabrous; lobes ovate-deltoid, c. 0.5 mm long, reflexed. Stamens 10, filaments c. 2 mm long, incurved at apex, pubescent throughout; anthers echinulate, broadly oblong, c. 0.8 mm long, tubule c. 1 mm long, dorsal appendages present, c. 0.5 mm long. Disk yellow, pubescent, hairs straight and as long those on calyx. Style white, cylindrical, c. 3.5 mm long. Fruit light green, turning yellow, dull, not shiny, cupular, 4.5–5.0 × c. 5.5 mm, base truncate, patently pubescent.

Distribution: —Endemic to the island of Sulawesi, Indonesia: Mount Sesean in North Toraja Regency, Eran Batu in Enrekang Regency, and Messawa in Mamasa Regency ( Figure 3 ).

Habitat and ecology: —On Mount Sesean, the new species occurs terrestrially in granitic bedrock areas in vegetation remnants near settlements to the open summit areas. It is common where it occurs, especially in the open summit areas. The plants in the vicinity include Dicranopteris Bernhardi (1805: 38) and Melastoma malabathricum Linnaeus (1753: 390) . In Eran Batu and Messawa the plants were found as epiphytes on tree trunks. The plants grow from 980 to 1920 m a.s.l.

Etymology: —The species is named after Dr. Graham Charles George Argent (1941–2019), a renowned expert on the Ericaceae of Southeast Asia, including Indonesia, who reinstated the genus Rigiolepis in 2019.

Phenology: —The plant flowers during November to December and fruits in November to December.

Proposed IUCN Conservation Status: —The three known populations of the species are threatened. The first and largest population is in Mount Sesean with around 10 individuals have been seen during the field studies. This population is located outside the protected areas of the government and we observed considerable threats from human activities. About one fifth of the individuals of the population were found to be growing in settled areas. Although we did not see any threats such as cutting, it is highly likely that many plants are susceptible to clearing such as farming activity is present in this area. The plants growing in the upper elevations are threatened by the presence of invading Merkus pine, Pinus merkusii Junghuhn & de Vriese in de Vriese (1845: 5) . We found almost no individuals of R. argentii growing under the pine stands. The available habitat of this species is highly likely to diminish, causing reduction in the species range. Mount Sesean is also a popular tourism site for hiking and camping and there have been forest fires and clear-cutting in the past (see also Helm and Farbarik 1998), and recently, newly built road for tourism also reaches the habitat of this species. The only undisturbed population restricted to the summit of Mount Sesean, with around 5 individuals exist. The second population in Messawa District occurs in highly disturbed forest that consists of at least 3 individuals growing on a tree. The last population that consists of one individual at Eran Batu, a limestone area, grows on a tree trunk near settlements and agricultural land and showed signs of reduction caused by severe anthropogenic disturbance. Following the categories and criteria from the IUCN (2012) and IUCN Standards and Petitions Subcommittee (2019), we provisionally categorize the species as Critically Endangered (D) due to the very small number of mature individuals.

Notes: —The new species is most similar to the morphologically variable Bornean species Rigiolepis moultonii . Argent (2019) designated three subspecies: R. moultonii subsp. moultonii , R. moultonii subsp. murudensis Argent (2019: 101) and R. moultonii subsp. muluensis ( Argent 2019: 101) . Rigiolepis argentii appears to be most similar to both subsp. muluensis and subsp. murudensis by its hairy floral disk. It differs from the subsp. muluensis by shorter style (3.5 mm vs. 5–5.5 mm) and from the subsp. murudensis by the non-glandular hairs on the calyx tube being more prominent than the glandular hairs (vs. glandular hairs more prominent). With the typical subsp. moultonii , R. argentii also differ in narrower leaf blades (≤ 41 mm wide vs. mostly ≥ 50 mm wide, pale yellow corolla (vs. pale cream to greenish-white). The number of flowers per inflorescence is rather fewer in R. argentii at mostly constant at 9–11 per inflorescence compared to a more variable range with 10–15 in R. moultonii .

In Sulawesi, only one other species of Rigiolepis has been described, R. henrici (Sleumer) Argent. This species differs from the new one in having a glabrous disk, narrower leaves (≤ 2 cm vs. (1.8–) 3.2–4.1 cm), and fewer lateral nerves ((1–)2 vs. 3–4). Rigiolepis argentii also differs from other specimens of Rigiolepis collected from Sulawesi and thought to represent undescribed species ( Argent 2019). It differs from de Vogel 5607 collected from Sopu Valley, Sulawesi Tengah Province by the plinerved pattern of venation (vs. predominantly pinnate), and from Hennipmann 6053 collected from Wawonseru Mountains, Soroako, Sulawesi Selatan Province by the habit (shrub vs. climber), the shorter distant basal marginal glands (1–2 mm from the petiole vs. 2.5–3.4 mm) and the longer pedicels (5.0– 7.3 mm vs. c. 2 mm).

Additional specimens examined (paratypes): — INDONESIA. Sulawesi Barat Province: Mamasa Regency, Messawa District (3°16′16.81″S 119°20′10.05″E), 980 m, 23 November 2019 (fl. bud), Ardi et al. 530 ( BO) . Sulawesi Selatan Province: Enrekang Regency, Eran Baru (3°28’4.10″S 119°54′35.62″E), 1166 m, 4 November 2018 (fr.), Ardi 335 ( BO) ; Toraja Utara Regency, village near Mount Sesean (2°54′57.91″S 119°52′13.46″E), 1324 m, 1 December 2019 (fl.), Ardi & Mustaqim 641 ( BO, CEB) ; Toraja Utara Regency, summit of Mount Sesean (2°53′51.12″S 119°52′40.93″E), 1920 m, 1 December 2019 (fl. & fr.), Ardi & Mustaqim 652 ( BO, CEB) .

Note: Characters of R. moultonii are based on the description, drawing, and photographs in Argent (2019) as well as a digital type specimen (Moulton 6676 (K000780639)).

Figures

FIGURE 1. Rigiolepis argentii Mustaqim & Ardi. A. Living plant. B. Flowering branchlet. Photos by Wendy A. Mustaqim.

FIGURE 2. Rigiolepis argentii Mustaqim & Ardi. A. Flowering branchlet with leaves in adaxial view. B. Branchlet with leaves in abaxial view. C. Inflorescences in bud. D. Inflorescence with some flowers open and others with corolla fallen. E. Flower. F. Stamen. G. Flower with corolla and stamens removed showing disk and style. H. Infructescences. I. Fruiting pedicel and fruit. J. Fruit, apical view. Scale bars: A–B = 2 cm; C = 1 cm; D = 5 mm; E = 1 mm; G = 2 mm; H = 5 mm; I–J = 2 mm.A, C, H based on Ardi et al. 652; B based on Ardi et al. 641; D, E, F, G, I, J based on Ardi et al. 342. Photos A, B, C, E, F, H by Wendy A. Mustaqim and D, G, I, J by Wisnu H. Ardi.

FIGURE 3. Distribution map of Rigiolepis argentii Mustaqim & Ardi. Map created with SimpleMappr, http://www.simplemappr.net (Shorthouse 2010).