Sonerila tenue J. Wai

Wai, Jarearnsak Sae & Hu, Jer-Ming, 2023, Twelve new species of Sonerila (Sonerileae, Melastomataceae) from Thailand, Phytotaxa 620 (2), pp. 107-142 : 138-141

12. Sonerila tenue J. Wai & J.-M. Hu, sp. nov. ( Figures 24 , 25 ).

TYPE:— THAILAND. NORTHERN: Uttaradit Province, Nam Pat District, Phu Soi Dao , 17°44’12.80” N, 100°59’21.23” E, 1600 m, 22 October 2016, J. Wai 2561 (holotype PSU!, isotypes BKF!, TAI!)

Diagnosis: Sonerila tenue is similar to S. collina Parker (1931: 42) in having isophyllous leaves with basal acrodromous venation, but differs by the slender stems (vs. stout woody stems), minute reddish brown glandular trichomes (vs. almost glabrous), shorter anthers (7–8.5 mm long vs. ca. 10 mm long).

Perennial herbs or subshrubs, 10–45 cm high; stems erect or ascending, slender, terete, simple or branched, semi-woody in older parts, 1–3 mm thick, almost all parts covered with minute reddish brown glandular trichomes, young parts usually reddish, old parts turn to grayish brown; internodes up to 3.5 cm long. Leaves opposite decussate, isomorphic, dark green or reddish purple, sometimes with a whitish stripe along the midvein, membranaceous when dry; petioles 0.5–3 cm long; blades elliptic, ovate or lanceolate, 1.5–8 × 1–3 cm, 1.5–4.3 times as long as wide, adaxially sparsely minutely strigose, abaxially sparsely minutely strigose along veins, apex acute to acuminate, base cuneate to rounded, margin shallowly serrulate; venation basal to subbasal acrodromous, usually with 3–5 main veins arising from the base. Inflorescences terminal or axillary, scorpioid cymes, 1–12-flowered, with scattered minute transparent brown glandular trichomes on peduncles, pedicels and hypanthia; peduncles erect or slightly curved, 1–2 cm long, reddish purple; bracts minute, triangular-oblong, 0.25–0.35 mm long. Flowers 3-merous; pedicels 3–5 mm long, purplish. Hypanthium cylindrical to obconical, 7–8.5 × 2.5–3 mm, purplish or greenish; part of hypanthium free from ovary 2.5–3 mm long. Calyx lobes 3, triangular-ovate, ca. 1.5 × 2.5–3 mm. Petals short-clawed, elliptic-ovate or elliptic-oblong, 11–13 × 6–7 mm, apex acuminate, pinkish, glabrous on both surfaces. Stamens 3, equal, glabrous; filaments 7–8.5 mm long, pinkish or white; anthers slightly incurved, deeply cordate at base, narrowing towards apex, 7–8.5 mm long, yellow, apex opening with two pores. Ovary 4–5 mm long, 3-locular; ovary crown ca. 1 mm high; ovules numerous; style 15–18 mm long, pinkish; stigma capitate, papillate. Capsule obpyramidal, trigonous, 7–8.5 × 4–5 mm. Seeds numerous, triangular ovoid, 0.5–0.6 mm long, ca. 0.3 mm wide, 0.2–0.25 mm thick (measured through SEM), dark brown; testa cells densely verrucose-papillose, with minute tubercles on antiraphal side; tubercles dome-shaped, with minute verrucose papillae on the top.

Paratypes:— THAILAND. NORTHERN: Uttaradit Province, Nam Pat District , Phu Soi Dao, 1566 m, 17 November 2009, M. Norsaengsri & S. Intamusik 6119 ( QBG!); ibid., 1570 m, 18 November 2009, M. Norsaengsri & S. Intamusik 6168 ( QBG!); ibid., 17°44’2.36” N, 100°59’56.80” E, 1613 m, 23 October 2016, J. Wai 2562 ( BKF!, PSU!, TAI!); Phu Miang , 1500 m, 16 February 1964, B. Hansen et al. 11173 ( SING!); North Side of Phu Miang , 1175–1550 m, 15 October 2005, J. F. Maxwell 05–572 ( BKF!, CMUB!). Phitsanulok Province, Chat Trakan District, Ban Romklao , 20 January 2009, C. Maknoi 2852 ( QBG!); Phu Soi Dao , 1800 m, 8 October 2008, W. Pongamornkul 3246 ( QBG!). NORTH-EASTERN: Loei Province, Na Haew District , Huai Nam Phak, 900 m, 9 December 1996, W. Nanakorn et al. 8004 ( QBG!); Phu Suan Sai , 1000 m, 25 April 1994, W. Nanakorn et al. 3068 ( QBG!); ibid., 5 November 1995, W. Nanakorn et al. 5140 ( QBG!); ibid., 1200 m, 10 December 1996, W. Nanakorn et al. 8069 ( QBG!); ibid., 17°30’ N, 100°56’ E, 950 m, 11 January 1998, P. Srisanga et al. 161 ( QBG!); ibid., 14 May 2008, C. Maknoi & P. Srisanga 2216 ( QBG!); ibid., 17°29’45.30” N, 100°56’56.70” E, 1225 m, 24 December 2015, J. Wai 2493 ( PSU!, TAI!); Phu Luang District, Phu Luang , 1100–1500 m, 4 December 1965, M. Tagawa et al. T1180 ( BKF!, KYO!); ibid., 900–1400 m, 6 December 1965, M. Tagawa et al. T1807 ( BKF!, KYO!, L!); ibid., 1250–1500 m, 17 November 1968, C. Chermsirivattana 1142 ( BK!); ibid., 23 November 2006, S. Watthana & H. Kurzweil 2170 ( BKF!, CMUB!, QBG!); ibid., 17°17’54.80”N, 101°31’24.90”E, 1383 m, 25 December 2015, J. Wai 2495 ( PSU!).

Distribution:— Thailand (Uttaradit, Phitsanulok and Loei Provinces). It might be also found across the border in Laos.

Habitat:— Terrestrial plant. This species was found growing in shaded areas of submontane to montane forests, at elevations of 900–1800 m.

Phenology:— Flowering and fruiting were observed from October to February.

DNA barcodes:— OP431284 (ITS), OP453067 (ETS), OP480565 (accD-psal), OP452991 (ndhF), OP480675 (rpl16), OP503782 (trnS-trnG), OP558271 (ndhC-trnV), OP495583 (ndhF-rpl32). All sequenced from J. Wai 2561.

Etymology:— The specific epithet “tenue” refers to the thin and slender habit of this species.

Vernacular name:—สาวสนมภู (Sao Sanom Phu) ( Thailand).

Proposed IUCN conservation status:— Endangered (EN) under criteria B1ab (iii)+B2ab (iii). This species is known only from four locations near Thai-Laos Border. The known extent of occurrence (EOO) is less than 5,000 km 2

and the known area of occupancy (AOO) is less than 500 km 2. Since they are particularly attractive to tourists and some populations are very close to nature trails, they have been partially disturbed by tourism activities. Therefore, we qualify this species as EN according to IUCN Red List guidelines Version 15.1 ( IUCN Standards and Petitions Committee 2022).

Figures

FIGURE 24. Sonerila tenue J. Wai & J.-M. Hu. A. Habit, B. Bract, C. Flower, D. Petals showing both adaxial (left) and abaxial (right) surfaces, E. Stamen, F. Longitudinal section of a flower showing hypanthium, stigma, style and ovary. G. Infructescence.All from J. Wai 2561 (PSU). Drawn by P. Tippayasri.

FIGURE 25. Photos of Sonerila tenue J. Wai & J.-M. Hu. A–B. Habit and habitat, C. Inflorescences, D. Fruits, E. Seed, lateral view, F. Seed showing verrucose papillae and tubercles on antiraphal side. Photos by J. Sae Wai.