Croton scalaeus J.Beyer, 2023

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 : 17-19

13. Croton scalaeus J.Beyer , sp. nov. — Fig. 5

Lepidote trichomes present instead of stellate trichomes on the leaves and stems, differing from other species with lepidote trichomes ( C. adumbratus , C. argyratus and C. cascarilloides ) in the not completely covered abaxial leaf side (still epidermis visible in C. scaleus ). Differs from C. cf. coriifolius based on larger and differently shaped stipules and small stalked leaf glands, whereas C. cf. coriifolius has larger and sessile leaf glands. Differs from C. laevifolius in the stellate trhichomes of up to 20 free radii, whereas the lepidote trichomes of C. scalaeus have more, 2–40, completely fused radii. The number of secondary veins in leaves of C. scalaeus is much higher than in the other species. — Type: Haviland & Hose 1846 (holo L [L.2212508]!; iso L [L.2212509]!), Malaysia, Sarawak,1st division,Kuching, 22 Feb.1952.

Paratypes: Buwalda 6681 (L [L.2203308]!), Indonesia, Sumatra, Riau, road from Sungei Berapit to Pekan Heran; George et al. S 58358 (L[L.2210922!]), Malaysia, Borneo, Sarawak, Sri Aman Div., Selepong Lop, Rumah Ungin; Pereira et al. 835 (L [L.2210921]!), Malaysia, Borneo, Sabah, Keningau, Nabawan, near Mukim Labau; Yates 2227 (L [L.2203859]!), Indonesia, Sumatra, Sumatera Utara,Asahan, Kwala Masihi.

Woody, shrubs or trees; young branchlets slightly pubescent, soon glabrescent. Indumentum consisting of lepidote trichomes on stems and leaves, 0.1–0.3 mm diam, flat, with 20–40 (very hard to count) fused radii, and stellate to stellate-lepidote trichomes on inflorescences, 0.2–0.3 mm diam, flat, with 8–15 free to slightly fused radii. Stipules linear, 3–8 by 0.5–1 mm, with scattered trichomes to slightly pubescent, caducous. Leaves pseudo-verticillate; petiole 1–4 cm long, deeply grooved above, with scattered trichomes; glands lateral on the very apex of the petiole, slightly stalked to sessile but elevated, 0.4–0.8 mm diam, stalk 0.1–0.5 mm long; blade elliptic to slightly obovate, 7.5–13.5 by 3–6 cm, 2–2.6 times longer than wide, chartaceous to subcoriaceous, symmetric, base attenuate to obtuse but with very base attenuate, margin subentire, with hair patches or glands, apex acuminate, adaxial side glabrous, abaxial side with scattered trichomes near base, apically subglabrous, epidermis visible; venation distinct, sunken above, basally not triplinerved, secondary veins 9–13 pairs, higher order veins distinct below. Inflorescences 1–4 per node, 6 –22 cm long, erect, basally up to 20 pistillate flowers, apically 1– 5 staminate flowers per node; axis sulcate, subglabrous; bracts triangular-ovate, c. 1.5 by 0.5 mm, (sub)glabrous except for patch of simple trichomes on apex, caducous. Staminate flowers 3–4 mm diam; pedicel c. 2 mm long, round, glabrous; sepals triangular-ovate, c. 2 by 1 mm, outside; petals oblong, c. 2.2 by 0.5 mm, lanate on margin near apex, trichomes point- ing inwards; stamens c. 11, free, filaments 2.5–3.5 mm long, anthers c. 0.5 by 0.3 mm. Pistillate flowers 3–3.5 mm diam; pedicel 2– 3 mm long, with scattered trichomes; sepals triangular-ovate, 1.5–1.8 by 1–1.5 mm, longer than ovary, (sub)- glabrous except for a small patch of simple trichomes on apex; petals absent; ovary obovoid, c. 2 by 2 mm, deeply sulcate, slightly to densely pubescent; style absent; stigmas c. 1.5 mm long, apically once divided to c. 1 mm from apex, glabrous. Capsules 3-lobed, obovoid, 3– 6 by 3– 6 mm, lobes conchiform, deeply sulcate, with scattered trichomes, apex depressed; pericarp c. 0.2 mm thick; columella c. 5 mm. Seeds ellipsoid, 5–6 by 3.5–4.5 mm, glabrous, with a small caruncle.

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

Habitat & Ecology — Primary and secondary forest, kerangas. Altitude: close to sea level. Flowering: September, February, April; fruiting: September.

Affinities — Unknown, as the sequence data are lacking, but morphologically highly similar to the 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 name — Ambin bua (Riau).

Note — The description is only based on two specimens from Sumatra, both with sparse inflorescences, and four specimens from Borneo. Distinctly different from other species in the C. oblongus complex by the presence of lepidote trichomes with a high number of fused radii instead of stellate trichomes with free radii .

Figures

Fig. 5 Abaxial leaf surface of Croton scalaeus J.Beyer showing the extra- floral nectaries and the lepidote trichomes. — 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.