Croton cf. coriifolius Airy Shaw

Beyer, J., Esser, H. - J., Eurlings, M. C. M. & Welzen, P. C. van, 2023, A revision of the genus Croton (Euphorbiaceae) in Sumatra (Indonesia), Blumea 68 (1), pp. 1-25 : 13

6. Croton cf. coriifolius Airy Shaw

Croton cf. coriifolius Airy Shaw (1974a) 311. — Type: Haviland ‘c.l.r.h.’ (holo K [ K000959189 ]*, iso SING!), Borneo , Sarawak, First Division, Matang.

Woody, probably tree or shrub, size unknown; young branchlets densely pubescent, soon glabrescent. Indumentum consisting of only stellate trichomes, yellowish to brown in the centre with whitish to yellowish radii, 0.1–0.4 mm diam (up to 0.6 mm on pistillate flowers), flat, often with a short central porrect radius, with 8–20(–30) free to rarely slightly fused radii. Stipules subulate to narrowly triangular, 2–4(–6) by 0.4–0.8 mm, subglabrous to slightly pubescent on both sides. Leaves pseudo-verticillate (occasionally almost alternate in lower parts); petiole 0.5–3.5 cm long, grooved above, sulcate, densely pubescent when young, soon glabrescent, (sub)glabrous when old; glands lateral on the very apex of the petiole, sessile, hardly elevated, 0.8–1.5 mm diam; blade narrowly elliptic to slightly obovate, 5.5–20 by 1.5–5 cm, (2.2–)2.7–4 times longer than wide, chartaceous to subcoriaceous (rarely membranous), base attenuate to cuneate (sometimes almost obtuse at very base), margin (sub)serrate, teeth 3–6 mm apart, often slightly revolute, without apical trichomes or glands, apex attenuate to acuminate, adaxial side glabrous, abaxial side slightly lighter when dried, with scattered trichomes when young (especially on midrib), later (sub)glabrous, epidermis well visible; venation distinct, not triplinerved, midrib sunken above, secondary veins 9–13 pairs, higher order nerves visible to distinct. Inflorescences terminal, 1–3(–5) per whorl, 6–19 cm long, (sub)glabrous, basally 8–20(–30) pistillate flowers, never staminate flowers at the same node as pistillate flowers, apically 1–3 staminate flowers per node; bracts triangular, 1–2.2 by 0.3–0.8 mm, (sub)- glabrous except for patch of simple trichomes on apex. Staminate flowers 2.5–3 mm diam; pedicel 2–3 mm long, round to slightly flattened, glabrous; sepals ovate, c. 1.5 by 1 mm, fused at base, outside glabrous; petals oblong, c. 1.6 by 0.3 mm, glabrous outside;stamens 8–11, free,filaments 1.7–2.2(–3.3) long, anthers c. 0.3 by 0.2 mm. Pistillate flowers 3.5–4.5 mm diam; pedicel 1–2 mm long (up to 3 mm in fruit), with scattered trichomes; sepals ovate, 1.8–3 by 1–1.5 mm, longer than ovary, outside with scattered trichomes, patch of simple trichomes on apex;petals absent;ovary obovoid to round,1.1–2by 1.2–1.6 mm, slightly sulcate, very densely whitish pubescent; style c. 0.3 (–0.5) mm long; stigmas 2.5–3.5 mm long, once divided, to 2–3 mm from apex. Capsules obovoid, 3–4 mm high, 3–5 mm diam, sulcate, apex slightly depressed, with scattered but distinct trichomes. Seeds unknown (on Borneo, type specimen: c. 4 mm wide), likely with a small caruncle.

Distribution — Malesia: Sumatra (Sumatera Utara, Riau, Jambi, Sumatera Seletan), Borneo ( Sarawak).

Habitat & Ecology — Altitude c. sea-level to 50 m. Flowering: March, April, October; fruiting: February.

Affinities — Part of the ‘ Riau pocket’ clade ( Fig. 1 : group I 4).

Vernacular name — Tjongheul (Jambi).

Note — Very limited material from Sumatra was found and none of the specimens had both staminate and pistillate flowers. Croton coriifolius is described from Borneo, where it only occurs in kerangas (heath) forests (low and species-poor forest on poor sandy soil; the last author has been there and has seen it). It is unclear where the Sumatran material was collected, and kerangas forest is not known from Sumatra (with the excep- tion of Banka and Biliton Islands), thus the identification of the Sumatran material has to be treated with caution (hence the cf. with the name). Many taxa have thicker leaves under the acid kerangas conditions, therefore Airy Shaw (1974a) indicates that this species might be a sclerophyllous ecotype of C. oblongus , which is a very doubtful species (see Discussion).

Figures

Fig. 1 Bayesian phylogram based on ITS sequences excluding the 5.8S region. The values at nodes represent the Bayesian-inference posterior-probability support values. Astraea and Brasiliocroton are outgroups. Black names: New World, yellowish brown: Africa–Madagascar, green: mainland Asia, blue: Aus- tralia–West Pacific,red: Malesia.Accessions with bold names correspond to the newly sequenced taxa, all ocurring in Sumatra. Bar: nucleotide substitutions.