Phyllagathis rivularis C.W. Lin, C.F. Chen & T.Y.A. Yang, 2017

Lin, Che-Wei, Chen, Chien-Fan & Yang, T. Y. Aleck, 2017, Ten new species of Phyllagathis (Trib. Sonerileae, Melastomataceae) from Sarawak, Borneo, Phytotaxa 302 (3), pp. 201-228 : 214-216

5. Phyllagathis rivularis C.W. Lin, C.F. Chen & T.Y.A. Yang , sp. nov. ( Fig. 10 , 11 ).

Type: MALAYSIA. Borneo, Sarawak, Sri Aman Division, Lubok Antu, Batang Ai, 100–300 m elev. Type specimen pressed from plants cultivated in a nursery in Hong Kong, 9 July 2014, C. W. Lin 564 (holotype TAIF).

Diagnosis: Phyllagathis rivularis is similar to P. elliptica in having an erect stem and an umbelliform inflorescence. However, the new species has panduriform-obovate (vs. elliptic to obovate) leaves 10.5–21 × 4.8–9 cm (vs. 4–15.5 × 2.2–7.8 cm); white petals (vs. pink or pale yellow); narrowly lanceolate anthers (vs. narrowly ovate); orbicular, non-ribbed capsules (vs. quadrangular, 8-ribbed), densely puberulous and velutinous (vs. glabrous or with sparse, long uniseriate hairs).

Caulescent herb, erect or ascending, terrestrial. Stems many branches, green, to 80 cm tall, 0.4–1 cm diam., terete, densely white tomentose or villose; internodes 3–8(–12) cm long. Leaf blades many, decussate, equal or slightly unequal, thick chartaceous, panduriform-obovate, 10.5–21 × 4.8–9 cm; base cordate, slightly auriculate, margins entire with rows of velutinous, apex attenuate to acuminate, sometimes obtuse; venation acrodromous, ca. 7 veined, 1 primary vein and 2 pairs of suprabasal secondary veins, often symmetrical at union with midvein, produced to 4.5 cm from the leaf base, positioned 1.3–2.2 cm in from margin at widest part of blade; veins slightly depressed on the adaxial surface and prominent on the abaxial surface, secondary and tertiary veins numerous and conspicuous, reticulate or slightly trellis-like; adaxially green, glabrous or glabrescent, velutinous on midrib and main veins, densely towards the base; abaxial surface pale green, densely tomentose and villose on all veins. Petioles 5–10 mm long, slightly grooved and flat terete, densely villose. Bracts persistent, green, ovate to widely ovate, 5–7 × 3–4.5 mm at the base of the inflorescence and becoming smaller upwards; adaxially glabrous, abaxially densely villose. Inflorescences in the upper leaf axils, umbelliform, peduncle 2.5–4 cm long, pale green, tomentose. Flowers tetramerous, pedicels 5–8 mm long, tomentose. Hypanthium campanulate, ca. 2.5–3 mm long and wide, puberulous and velutinous outside, sometimes with minute glands. Sepals 4, persistent, widely triangular, connate into a rim, each lobe with a caudate, angled, triangular keel up to 1.5 mm long. Petals 4, oblique, ovate, 3–4.5 × 1.5–2.2 mm, white, glabrous, apex acuminate to apiculate. Stamens (residual): 8, isomorphic, subequal, filaments slightly flat, 2.5–3.5 mm long, white, anthers narrowly lanceolate, apex attenuate, ventrally curved, ca. 3 mm long, pore 1, connective distinct, dorsally with an inconspicuous tuberculate appendage, apex retuse. Style filiform, white, ca. 7 mm long, glabrous, stigma capitate. Ovary 2/3–3/4 as long as the hypanthium, crown lobes large, with connate lobes, margins sparsely denticulate, anther pockets shallow, placentae stalked. Capsules on pedicels up to 1 cm long. hypanthium cup-shaped, non-ribbed, 3–4 × 3–3.5 mm, placentae disintegrating after seed dehiscence.

Distribution and ecology: Endemic to Batang Ai area, Sarawak ( Fig. 3 ), on riverbanks and steep slopes in deep to slightly shaded lowland mixed dipterocarp forest, at 100 to 300 m elevation. It is quite common in upstream Batang Ai area.

Etymology: rivularis means “river”, and the epithet refers to the fact that the new species grows along stream banks.

Figures

FIGURE 3. Distribution maps of Phyllagathis lii, P. millelunata, P. rivularis, P. rubrosetosa, P. ulu, (stars); P. phyllioides, P. violinifolia, P. yodae (solid circles); P. bicolor (solid triangles); P. wallacei (solid squares) in Sarawak, Borneo.

FIGURE 10. Phyllagathis rivularis C.W. Lin, C.F. Chen & T.Y.A. Yang. A. Habit; B, B’. Bracts, abaxial and adaxial view; C. Petal; D. Stamen, side view; E. Style; F. Vertical section of the ovary; G. Capsule, side view.All from C.W. Lin 564 (TAIF).

FIGURE 11. Phyllagathis rivularis C.W. Lin, C.F. Chen & T.Y.A.Yang. A. Habit and habitat; B, C. Inflorescence; D. Hypanthium, apical view. D from C.W. Lin 564 (TAIF).