Croton heterocarpus Müll.Arg.

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 : 15

9. Croton heterocarpus Müll.Arg. — Fig. 2a

Croton heterocarpus Müll.Arg. (1866) 621; Hallier f. (1911) 7; Merr. (1921a) 337;(1923) 425;Ridl.(1924) 262 (‘ heteropetalum ’); Merr.(1926) 382; Whitmore (1973) 85; Airy Shaw (1975) 93; (1981a) 285;(1983) 18; Corner (1988) 284. — Oxydectes heterocarpa (Hook.f.) Kuntze (1891) 612. — Lectotype (designated here): Zollinger 3982 (lecto L [L 0234540]!, Herb. Hasskarl; isolecto G-DC [G00312279]!, W [W 1889-0024627]!, [W 1889-0024628]!), Sumatra, Prov. Lampong, River Toelang Bawang.

Croton ardisioides Hook.f. (1887) 393;Merr. (1909) 278. — Oxydectes ardisiodes (Hook.f.) Kuntze (1891) 614. — Lectotype (designated here): Griffith KD 4783 (lecto K [K000959156]*; isolecto CAL [CAL0000023600]*, GH [00100136]!, P [P00623696]!), Malacca. Other syntype Griffith s.n. (CAL [CAL0000023620]*, K [K000959157]*, P [P00623695]!), Malacca. ( Hooker (1887) indicates as collecting locality Borneo, but all specimens show Malacca).

Trees, to 12 m tall, diam to 35 cm; young branchlets densely pubescent,soon glabrescent,scar tissue very common on branches and between whorls of leaves. Outer bark smooth, brownish. Indumentum consisting of yellowish brown stellate trichomes, 0.2–0.4 mm diam, flat, with c. 10–25 free radii, and patches of erect simple trichomes, c. 0.5 mm long. Stipules ensiform to triangular, 2–4 by 0.5–1 mm, densely pubescent on both sides. Leaves alternate in lower parts, pseudo-whorled apically, with every branch ending with a whorl of leaves and inflorescences; petiole 0.5–2 cm long, round at base, upwards soon flattened to apically with an adaxial sharp groove, trichomes scattered; glands adaxially on the very apex of the petiole, sessile but slightly elevated (less than 0.5 mm high), 0.3–0.6 mm diam ( Fig. 2a ); blade obovate (to elliptic), 2.5–10(–12) by 1.2– 4.1 cm, 1.9–3 times longer than wide, membranous to chartaceous, base attenuate to cuneate, margin serrate to slightly crenate, teeth 2–5(–7) mm apart, patches of erect trichomes on apex of teeth, apex acute to nearly rounded, adaxial side glabrous, abaxial side subglabrous with very few scattered trichomes, glabrescent, epidermis well visible; venation distinct, sunken above, basally not triplinerved, secondary veins 6 –10 pairs, higher order veins visible. Inflorescences 2–4 per node, 5–20 cm long, erect, greenish white, basally 6–14 pistillate flowers, staminate flowers never on same node as pistillate flowers; bracts triangular-ovate, c. 1 by 1 mm, eglandular, glabrous except for patch of simple trichomes on apex, quite persistent. Staminate flowers c. 3 mm diam; pedicel c. 1 mm long, round to slightly flattened, sulcate, glabrous; sepals ovate, c. 1.5 by 1 mm, subglabrous outside; petals oblong, c. 1.2 by 0.4 mm, outside glabrous, inside and margin lanate; stamens 8 –12, free, filaments c. 2 mm long, anthers c. 0.5 by 0.4 mm. Pistillate flowers c. 3 mm diam; pedicel 0.5–1 mm long, subglabrous; sepals oblong to ovate, 1.5–2 by c. 1 mm (up to 2.5 by 1.5 mm in fruit), fused at the very base, subglabrous but on the very apex a patch of simple trichomes, slightly longer than ovary; petals absent; ovary globose, 1–1.5 by 1–1.5 mm, very densely yellowish pubescent; style less than 0.1 mm long; stigmas 2–2.5 mm long, free and thickened at base, once divided to 1.5–2 mm from top. Capsules obovoid, c. 5 mm high, c. 5 mm diam, slightly sulcate, surface rough, with scattered trichomes, green (immature); pericarp c. 0.5 mm thick; columella c. 5 mm long. Seeds obovoid, flattened on inner side, c. 3 by 3 mm, glabrous, carunculate.

Distribution — Malesia: Malay Peninsula, Sumatra (Sumatera Utara, Lampung), Borneo, Philippines, Moluccas.

Habitat & Ecology — In primary forest, mangroves, swamp forests and on riverbanks, always near water. Altitude: sea level to 90 m. Flowering: unknown for Sumatra; fruiting: August .

Affinities — Croton section Furcaria ( Webster 1993) . Croton heterocarpus groups together with C. macrocarpus ( Fig. 1 : group I 1), which might also be classified in this section, though the sections of Webster (1993) are not always recognized after phylogenetic analyses.

Vernacular names — Borneo: Djingah berkosah.

Uses — Roots are used as medicine in Sabah (N Borneo, Neil 7064).

Figures

Fig. 2 Different types of leaf glands. a. Croton heterocarpus, glands sessile and placed more adaxially on the apex of the petiole; b. C. caudatus, glands 1–3 pairs, distinctly stalked and abaxially on the midrib base; c. C. viridifolius, glands slightly stalked and located either on the leaf blade base or as in drawing on the side veins; d. C. macrocarpus: glands with a thick stalk located on the midrib base; e. C. adumbratus: glands sessile on the midrib base (a: LÖrzing 13830; b: Forbes 2989; c:Kleinhoonte 460; d:de Wilde & de Wilde­Duyfjes 20590; e:de Wilde & de Wilde­Duyfjes 19604; all L). — Illustration by Esmée Winkel,2021.

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.