Croton laevifolius Blume, 1826

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 : 16

11. Croton laevifolius Blume

Croton laevifolius Blume (1826) 603 (‘ laevifolium’); Müll.Arg. (1866) 619; J.J.Sm.(1910) 341;Merr.(1921a) 337; Corner (1939) 294; Whitmore (1973) 85. — Lectotype (designated here): Blume 1473 (lecto L [L.2203878]!; isolecto L [L. 2203879]!), Indonesia, Java.

Croton diadenus Miq.(1861) 451,180 (‘ diadenum ’), p. 451 contains description and type,p. 180 vernacular name. — Type: Teijsmann HB 3499 (holo U [ U 0001893 ]!, likely iso G-DC (without number) [ G00312289 ]!), Indonesia, Bangka , prope Djebus.

Croton korthalsii Müll.Arg. (1866) 527. — Type: Korthals s.n. (holo L [L.2203684]!), Indonesia, Borneo .

Mallotus minahassae Koord. (1898) 626. — Lectotype (designated here): Koorders 196453 (lecto L [L.2203657]!), [ Indonesia,] Celebes, Prov. Minahasa, Menado , 1895.

Croton oreoborneicus Croizat (1942b) 496. — Type: Agama 568 (holo A [ A00047515 ]!), British North Borneo.

Croton oblongus auct. non. Burm.f: Merr. (1921b) 361 (‘ oblongum ’); (1929) 156, p.p.; Backer & Bakh.f. (1963) 476, p.p.; Airy Shaw (1975) 94, p.p.; (1981a) 285, p.p.; (1982a) 15, p.p.; Govaerts et al. (2000) 449, p.p. See note.

Treelets, 3–8 m tall, diam c. 6 cm, young branchlets slightly pubescent, soon glabrescent. Indumentum consisting of stellate trichomes only, yellowish brown in the centre with whitish radii, 0.1–0.4 mm diam, often with a central porrect radius, with 11–20 free to basally slightly fused radii. Stipules subulate, 2–5(–7) by 0.5–1 mm, outside slightly pubescent (occasionally subglabrous), inside densely pubescent (occasionally subglabrous), quite persistent to caducous. Leaves alternate to pseudo-verticillate; petiole 1–5 cm long, deeply grooved above, subglabrous; glands abaxially (sometimes almost adaxially) on the very apex of the petiole, sessile but elevated to slightly stalked, 0.3–0.6(–1) mm diam, stalk 0.1–0.5(–1) mm high; blade obovate to elliptic (rarely ovate), 5–17 by 3–7 cm, 1.7–3 (–3.5) times longer than wide, chartaceous, base cuneate to obtuse, margin slightly serrate (teeth without trichomes or glands) to almost entire, apex acuminate, adaxial side glabrous, abaxial side lighter when dried, subglabrous to glabrous, epidermis visible; venation distinct, sunken above, basally not triplinerved, secondary veins 7–10 pairs, higher order veins reticulate. Inflorescences terminal to axillary (always near apex), (1–)2–6 per apical node, 5–23 cm long, erect, basally (2–)5–20(–26) pistillate flowers, sometimes completely staminate, rarely 1–3 staminate flowers at same node as a pistillate flower, apically 1–3(–5) staminate flowers per node; bracts triangular-ovate, 0.8–2 by 0.4–1 mm, glabrous to slightly pubescent, often with a small patch of simple trichomes on apex, quite persistent (especially with staminate flowers). Staminate flowers 3–3.5 mm diam; pedicel 0.8–3 mm long, round, glabrous to subglabrous; sepals ovate, 1.2–2 by 0.9–1.2 mm, fused at base, glabrous to subglabrous; petals oblong, 1.7–2.1 by 0.3–0.5(–1) mm, always slightly longer than sepals, glabrous except for small patch of simple trichomes on apex; stamens 10 or 11, free, filaments 1.5–2 mm long, anthers c. 0.5 by 0.4 mm. Pistillate flowers 3–4.5 mm diam; pedicel 1–3 mm long (up to 4 mm in fruit), glabrous to slightly pubescent; sepals triangular-ovate, 1.8–2 by 1–1.5 mm, fused at very base, longer than ovary, with scattered trichomes (denser near base) to glabrous except for a small patch of simple trichomes at the apex; petals oblong, c. 1.2 by 0.3 mm, usually absent; ovary obovoid, c. 1.5 by 1.5 mm, deeply sulcate, very densely yellowish pubescent, style 0.2–0.4 mm long; stigmas 2–3 mm long, thickened at base, once divided to 1.5–2 mm from apex. Capsules distinctly 3-lobed, obovoid, 5–8(–13) mm high by 4–7 mm diam, sulcate, apex slightly depressed, with scattered but distinct trichomes; pericarp 0.3–0.5(–1) mm thick; columella 4–6 mm long. Seeds obovoid to almost prolate, 5–6(–8) by 3–4(–6.5) mm, glabrous, with a small caruncle.

Distribution — Malesia: Sumatra (Sumatera Barat, Riau, Sumatera Selatan, Banka-Belitung), Java, Borneo, Sulawesi, Lesser Sunda Islands.

Habitat & Ecology — In rather open primary or secundary forest. On clayey, sandy soil or granitic sand. Altitude: 0–1000 m. Flowering: August–January, April; fruiting: May.

Affinities — No sequence data are available, but morphologically highly similar to species in the ‘ Riau pocket’ clade ( Fig. 1 : group I 4), based on the lack of colleters and similarities in trichomes and leaf shape.

Vernacular names — Kelangin (Banka-Belingtung).

Note ― Croton laevifolius is considered to be a synonym of C. oblongus (see Discussion; e.g., Airy Shaw1982a). Croton oblongus forms a species complex from which various species could be split off for Sumatra. This complex needs further study in the remaining distribution area.

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.