Microcos riparia (Boerl. & Koord.) Burret

Chung, R. C. K. & Soepadmo, E., 2011, Taxonomic revision of the genus Microcos (Malvaceae-Grewioideae) in Peninsular Malaysia and Singapore, Blumea 56 (3), pp. 273-299 : 295

11. Microcos riparia (Boerl. & Koord.) Burret — Fig. 12 ; Map 2

Microcos riparia (Boerl. & Koord.) Burret (1926) 795; Whitmore & Tantra (1986) 241; R.C.K. Chung et al. (2005b) 118. — Grewia riparia Boerl. & Koord. (1911) 35. — Type: Koorders 10450 (holo BO), Sumatra.

Microcos ovato-lanceolata Burret (1934) 163. — Type: Hallier 1314 (BO, 3 sheets), Borneo, Kalimantan, Sungai Keniboeng .

Small tree. Twigs smooth or slightly striate, black, covered with minute stellate hairs when young, greyish brown to brown, glabrous when older. Stipules early caducous. Leaves dull brown above, brown beneath, subcoriaceous, glabrous above, glabrous or sparsely covered with minute stellate hairs beneath; petioles (10 –)11–15(–17) mm long, 1–1.5(– 2) mm thick, brown to dark brown, apically swollen for 6 –10 mm long, densely covered with minute stellate hairs above, basally sparsely covered with minute stellate hairs; blade lanceolate or ovate to broadly ovate, equilateral or sometimes inequilateral, (11–)12– 20(–22) by (4–)5 –7(– 8) cm, base obtuse to rounded or truncate, margin distantly serrulate or undulate and rarely entire, not ciliate, apex acuminate, acumen 1–2 cm long with a blunt tip; midrib raised on both sides; secondary veins 5 –7 pairs, flattened above, raised beneath, basal pair reaching almost or more than 0.5 of blade length, forming an angle of 45° with the midrib; hairy pocket-type domatia present beneath in axils of basal vein pair as well as other veins; tertiary veins reticulate, inconspicuous above, conspicuous beneath. Inflorescences Type B panicles, terminal or axillary, (3–) 6 – 8 cm long, covered with minute stellate hairs; bracts early caducous; involucral bracts of outer whorl 4 – 5.5 mm long, 2 – 3-parted, lobes lanceolate, 3 – 4 mm long, apex acute, smooth outside, densely covered with stellate hairs on both sides, that of inner whorl narrowly elliptic or narrowly oblong, 4 – 4.5 by 0.6 –0.9 mm, apex acute, densely covered with stellate hairs on both sides. Flower buds oblong, 4– 6 by 2.5 –3.5 mm, densely covered with stellate hairs; pedicels 0.5–1.2 mm long, 0.7–1 mm thick, densely covered with stellate hairs; sepals lanceolate, 6–7.5 by 1–1.3 mm, densely covered with stellate hairs outside, sparsely covered with stellate hairs towards the apex inside; petals 5, narrowly oblong or lanceolate, 2.5– 3.5 by 0.7–1 mm, apex shallowly 2-lobed, outside densely covered with stellate hairs at base to c. 0.5 of its length and sparsely covered with glandular trichomes towards the apex, inside densely covered with stellate hairs around the glands to c. 0.5 of its length and sparsely covered with glandular trichomes towards the apex; glands ellipsoid; androgynophore concave in outline, 1.5 – 2 mm long, 0.5 –1.2 mm diam, shallowly longitudinally grooved, glabrous, apical part expanded into a flat disc-like structure of c. 0.3 mm wide, with undulate rim covered with stellate hairs; stamens with filaments 2.5–3.5 mm long, glabrous, anthers c. 0.3 mm diam; ovary 3-locular, globose to subglobose, 0.8–1.2 mm diam, circular in cross section, sparsely covered with stellate hairs; style 3.5 – 4 mm long, sparsely covered with stellate hairs at base to reaching between 0.25 and 0.5 of its length and glabrous towards the apex. Infructescences glabrous. Fruits pyriform, smooth, 2.5 – 2.7 by 1.4 –1.8 cm, drying brown-black to dark black, glabrous; apex rounded, pseudostalk narrowed, 5–7 mm long; exocarp membranous; mesocarp 5– 6 mm thick; endocarp c. 0.5 mm thick, woody. Fertile pyrene 1, 1-seeded, 8–10 mm long; sterile pyrene thin, inconspicuous.

Distribution — Sumatra, Peninsular Malaysia (only recorded from Rompin FR, Pahang) and Borneo ( Sarawak and E Kalimantan).

Habitat & Ecology — Alluvial forest near or along rivers, at low elevation. Flowering:April– May, September; fruiting: March, September, December.

Vernacular names — Damak-damak, damak-damak air, labulabu (Malay).

Note — A few collections (Mahamud FMS 17156, Soh FMS 15476, Yeob FMS 3190 and FMS 3237) from Peninsular Malaysia were previously wrongly identified as M. laurifolia . These specimens belong to M. riparia .

Figures

Map 2 Distribution of Microcos erythrocarpa (Ridl.) Airy Shaw ($) and M. riparia (Boerl. & Koord.) Burret (:) in Peninsular Malaysia.

Fig. 12 Microcos riparia (Boerl. & Koord.) Burret. a. Leafy twig; b. detail of abaxial leaf surface near base with hairy pocket-type domatia in the axils of basal pair of secondary veins; c. inflorescence; d. flower buds surrounded by involucral bracts; e. longitudinal section of flower bud; f. flower with sepals and petals removed; g. adaxial surface of sepal; h. abaxial surface of petal; i. adaxial surface of petal with gland at base; j. stigma; k. fruit; l. longitudinal section of fruit; m. cross section of fruit (a, b, e–j: Hallier 2208; c, d: Yeob FMS 3190; k–m: Mahamud FMS 17156). — Drawn by J. Pao, SAR.