Croton macrocarpus Ridl.

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 : 16-17

12. Croton macrocarpus Ridl. — Fig. 2d

Croton macrocarpus Ridl. (1925) 332 (non Rchb. ex Müll.Arg. (1866) 698, nom. nud.). — Croton grandifructus Radcl. - Sm. & Govaerts (1997) 187, nom. superfl., see note 2. — Lectotype (designated here): I.H. Burkill 6519 (lecto K [ K000959163 ]*;isolecto A [00105623]*), Malaysia, Selangor, Telok Forest Reserve , Klang.

Treelets, c. 6 m tall, dbh c. 10 cm; young branchlets densely pubescent,hardly glabrescent. Indumentum consisting of creamy to amber stellate trichomes with a darker brown centre, 0.3–0.6 mm diam (up to 1.2 mm on ovary), often slightly porrect, with one short central radius and 6–12 free radii. Stipules ensiform to subulate, 5–8 by 0.5–0.8 mm, densely pubescent on both sides, soon caducous. Leaves alternate; petiole (3–) 6–13 cm long, round, slightly sulcate, at most slightly grooved above, densely to slightly pubescent; glands 1 or 2 pairs of distinctly stalked discs, lateral abaxially on the very apex of the petiole, 0.5–1 mm diam, stalk 0.3–1 mm long ( Fig. 2d ), additional smaller marginal glands common, 0.3–0.6 mm diam, stalk 0.2–0.5 mm long; blade elliptic, 15–30(–35) by 5–10 cm, 2.8–3.6 times longer than wide, chartaceous to subcoriaceous, base subcordate, margin (sub)serrate, teeth 2–6 mm apart, apex acuminate, adaxial side glabrous, but midrib pubescent, abaxial side slightly to densely pubescent, surface always visible except in very young leaves; venation distinct, raised on both sides, basally not to indistinctly triplinerved, secondary veins 13–17 pairs, higher order veins distinct on both sides. Inflorescences 1–4 per node, 11–35 cm long, erect, densely pubescent all over, basally 20– 30 pistillate flowers, rarely 1–2 staminate flowers in the cymule of a pistillate flower, apically 1–4 staminate flowers per node; bracts narrowly triangular, 2–3.5 by 0.5–1.5 mm, outside with scattered trichomes, with a patch of simple trichomes on apex, inside glabrous, soon caducous. Staminate flowers 5–6 mm diam; pedicel 3–9(–11) mm long, round, densely pubescent; sepals triangular-ovate, c. 2.5–3 by 1.5–2 mm, outside pubescent near base to glabrous near apex, inside glabrous; petals oblong, 2–2.3 by 0.7–1 mm, outside glabrous; stamens c. 15, free, filaments 3–4 mm long, anthers c. 1 by 0.5 mm. Pistillate flowers 10 –13 mm diam; pedicel c. 4 mm long (to 10 mm in fruit), sulcate, densely pubescent; sepals triangular-ovate to narrowly triangular, 4.5–6 by 2– 3 mm, outside densely to slightly pubescent, with a patch of short simple trichomes on apex, much longer than ovary; petals triangular-ovate to ensiform, 2–2.5 by 0.4–0.7 mm, outside densely pubescent, hispid on margin and apex, not caducous; ovary globose, 3.5–5 by 3–4 mm, densely yellowish hispid, style absent, stigmas c. 7 mm long, once divided to c. 5.5 mm from apex, slightly pubescent near base. Capsules cylindrical globose, slightly trilobate, c. 28 mm high, c. 22 mm diam, sulcate, densely pubescent; pericarp very thick (c. 1.5 mm) and woody; columella c. 23 mm long. Seeds obovoid, heavily flattened, c. 19 by 13 mm, with a groove on the inside, glabrous, carunculate.

Distribution — Malesia: Malay Peninsula, Sumatra (Aceh).

Habitat & Ecology — Partly logged-over forest, dry land forest on rolling hills, yellow-red loamy soil. Altitude: c. 30– 40 m. Flowering: August; fruiting: August.

Affinities — Related to C. heterocarpus ( Fig. 1 : group I 2) and should be classified in C. section Furcaria ( Webster 1993) , though that section still has to be corroborated phylogenetically.

Notes — 1. Only one collection from Sumatra (de Wilde & de Wilde­Duyfjes 20590, L) and one from the Malay Peninsula (Burkill 6519, A, K).

2. Radcliffe-Smith & Govaerts (1997) assumed that Müller’s name (1866) was correct and regarded Ridley’s name ( Ridley 1925) as a later incorrect homonym. However, Müller only noted the name without a description, which makes it an invalid name. Therefore, Ridley’s name is correct and Radcliffe-Smith & Govaerts created a superfluous name (see Esser 2002a: 21).

3. Two sequences, duplicates of the same collection, were used in the phylogenetic analysis.These showed up as a trichotomy in the cladogram ( Fig. 1 ) with one specimen of C. heterocarpus . However, the branches leading to the two entries of C. macrocarpus are very short, which proves that they belong to the same specimen indeed.

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.