Malesian Euphorbiaceae Descriptions
Welzen, P.C. van. 1998. Revisions and phylogenies of Malesian Euphorbiaceae: Subtribe Lasiococcinae (Homonoia, Lasiococca, Spathiostemon) and Clonostylis, Ricinus, and Wetria. Blumea 43: 131–164.
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Clonostylis is provisionally treated as a monotypic genus based on C. forbesii. Only one specimen with pistillate flowers is known, it was collected by Forbes from Sumatra. Clonostylis is not a synonym of Spathiostemon (see introduction under the latter genus). The correct classification of this genus will have to wait till staminate flowers and fruits are known. It might be close to or a species in Mallotus or Macaranga.
Clonostylis S.Moore, J. Bot. 63, Suppl. (1925) 101; Pax & K.Hoffm. in Engl. & Harms, Pflanzenfam. ed. 2, 19c (1931) 229; Airy Shaw, Kew Bull. Add. Ser. 4 (1975) 4, 14; Kew Bull. 32 (1978) 407 (in synon.); Kew Bull. 36 (1981) 345 (in synon.); Welzen, Blumea 43 (1998) 150; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11 (2014) 129 (sub Spathiostemon). — Type: Clonostylis forbesii S.Moore
Trees, dioecious?; flowering twigs smooth, glabrous. Indumentum existing of simple hairs only. Stipules unknown. Leaves spirally arranged (to opposite), simple; petiole relatively long, reniform in transverse section, basally and apically somewhat pulvinate; blade parchment-like, symmetric, green when dry, above and below with submarginal circular glands, base attenuate, margin entire to somewhat sinuate, sometimes with glands in the undules, apex acuminate, very apex acute, venation raised on both sides, basally 3-nerved, nerves looped and joined near margin, usually with a few hair dot domatia, veins scalariform, quaternary veins reticulate. Pistillate inflorescences axillary racemes, one or two per axil, round, grooved, erect, sericeous, with 1 or 2 opposite flowers per node. Staminate flowers unknown. Pistillate flowers actinomorphic, sessile; sepals bract-like, 5 or 6, in two whorls, outside sericeous, inside glabrous; petals and disc absent; pistil 3-locular, ovoid, angular, tapering into the style, smooth, sericeous, one ovule per locule; style short, stigmas 3, upper twothird split, sericeous, but above papillate. Fruits unknown.
Distribution — A single species is known from Sumatra.
Clonostylis forbesii S.Moore, J. Bot. 63, Suppl. (1925) 101, fig. — Spathiostemon forbesii (S.Moore) Airy Shaw, Kew Bull. 32 (1978) 407; Kew Bull. 36 (1981) 345, p.p., type only; Welzen, Blumea 43 (1998) 151. — Type: Forbes 3027 (BM, holo; iso in A), Sumatra, Palembang, Moeara Mengkoelem, R. Rawas.
Tree; flowering twigs 1.5–2 mm thick. Leaves: petiole 2.4–3.7 cm long, glabrous; blade elliptic, 8.4–13.5 by 3.5–6 cm, ratio 2.3–2.4, smooth and glabrous on both sides, venation with c. 5 pairs of nerves. Pistillate inflorescences up to 3 cm long. Pistillate flowers: sepals triangular to ovate, c. 1.3 by 1.5 mm, thick; pistil 2.5–2.8 by 2.3–2.5 mm; style 0.7–0.8 mm long; stigmas 5–5.5 mm long, upper 2.4–3.8 mm dichotomous.
Distribution — Endemic on Sumatra, but only known from the type specimen.