Croton adumbratus Croizat

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 : 8

1. Croton adumbratus Croizat — Fig. 2e , 3a–c

Croton adumbratus Croizat (1942b) 495; Esser & Veldkamp (2008) 167, f. 1a–c. — Holotype: Griffith s.n. ‘Malacca’ (holo GH [00047509]!; iso CAL n.v., CGE n.v., K [K000959164]*, [K000959165]*, L [L 0233476]!, [L 0233442]!, M [M-0241965]!, P [P00623698]*), Malacca.

Croton argyratus auct.non Blume: Müll.Arg. (1866) 526,p.p.; Hook.f.(1887) 385, p.p.; Ridl. (1924) 260, p.p.; (‘ argyratum ’); Whitmore (1973) 85, p.p.

Croton erythrostachys auct. non. Hook.f.: Airy Shaw (1981a) 284, p.p.; Govaerts et al. (2000) 449, p.p.

Trees or shrubs, up to 15 m tall, dbh up to 60 cm; young branchlets densely pubescent, hardly glabrescent. Outer bark smooth, whitish grey to pale dark green; inner bark pinkish to red. Indumentum consisting of lepidote trichomes on leaves to stellate-lepidote trichomes on stems, diam 0.2–0.3 mm on leaves, 0.3–0.5 mm on stems, flat, with 25–40 fused radii (c. 20 free to fused radii on young branchlets), with small brownish centre (then appearing silvery-hyaline) or brown throughout. Stipules filiform to subulate, (2–)4–10 by 0.2–1 mm, densely pubescent on both sides, caducous. Leaves alternate; petiole 1.5–5(–7) cm long, slightly grooved above, densely pubescent, sulcate; glands abaxial as flat discs lateral on the very base of the midrib, (0.1–)0.5–0.9 diam, sessile but distinct ( Fig. 2e ); blade elliptic to slightly ovate, 6–21 by (2–) 3.5–8.5 cm, (2–) 2.4–3.5 times longer than wide, membranous to chartaceous, base cuneate with the very base rounded to subcordate, margin entire, apex acuminate, adaxial side glabrous (rarely with scattered trichomes on young leaves), abaxial side very densely and completely silvery to brownish pubescent with the surface not visible; venation distinct, sunken above, basally not to slightly triplinerved, lateral veins 6–10 pairs, higher order nerves distinct. Inflorescences racemose, 1(–3) per node, (5–)8–12(–15) cm long, erect, bisexual (occasionally one sex only), white to greenish, densely pubescent all over, basally 3 – 8 pistillate flowers, apically 20 or more staminate flowers; bracts triangular-ovate, 1–1.5 by 0.5–1 mm, densely pubescent outside, inside subglabrous. Staminate flowers 4–5 mm diam; pedicel 2–3 mm long, round, densely pubescent; sepals ovate, 2–2.5 by 1–2 mm, densely pubescent outside, lanate on margin; petals triangular-ovate, 2–2.5 by 0.8–1.5 mm, outside subglabrous; stamens 9–11, free, filaments 2–3 mm long, anthers c. 1 by 0.4 mm. Pistillate flowers 4.5–6 diam; pedicel 1–5 mm long, sulcate, densely pubescent; sepals ovate to almost oblong, 2.5–4 by 1.3–2 mm, fused at base, longer than ovary, outside densely pubescent, inside with scattered trichomes; petals ensiform, c. 2 by 0.5 mm, usually absent; ovary subglobose, 1.5–2.5 by 1.5–2 mm, densely yellowish brown pubescent; style 0.2–0.5 mm long, densely pubescent; stigmas 3–5 mm long, once divided to 2.5–4 mm from apex, pubescent near base. Capsules globose, 5–7 mm high by 6–7 mm diam, hardly sulcate, densely pubescent, apex sunken; pericarp c. 0.3 mm thick; columella 5–7 mm long. Seeds ellipsoid, flattened, 5–7 by 4–5 mm, glabrous, with a small carunculate.

Distribution — Malay Peninsula, Sumatra (Aceh, Sumatera Utara, Sumatera Barat, Jambi, Sumatera Selatan, Bangka- Belitung), Borneo (Kalimantan Barat) and Sulawesi.

Habitat & Ecology — Primary and secondary lowland forests. Altitude: sea level to 750 m, often on sandstone but also on limestone hills. Flowering: March–April, July–August, October–November; fruiting: March, July, October.

Affinities — Based on the phylogenetic analysis and similar morphology to be classified in Croton section Argyrati ( Van Ee et al. 2015) .

Vernacular names — Bali anghiri (Simalungen), Kayu bulan (Sumatera Selatan), Kayu semangkil (Bangka).

Note — Several plants were collected with galls (Krukoff 4022, 4281; De Wilde & de Wilde­Duyfjes 20147). These leafy galls, looking like Brussels sprouts, seem to be very characteristic for C. adumbratus and are not seen in any other Croton from Western Malesia ( Esser & Veldkamp 2008); other collections with galls (not seen, from other areas): Alvins 264, KEP (Abdullah) 33070.

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. 3 a–c. Croton adumbratus Croizat. a. Habit; b. detail of cuneate leaf base, abaxial view; c. fruit. — d–f. Croton argyratus Blume: d. Habit; e. detail of narrowly emarginate leaf base, abaxial view; f. fruit (a–c: de Wilde & de Wilde­Duyfjes 19604; d–f: Chellia KEP 104397; all L). — Illustration by Anita Walsmit Sachs, 2007.