Flora of Thailand Euphorbiaceae

 

46. Homalanthus

 

H.-J. Esser & P.C. van Welzen

 

Goto on this page:

Genus description

Species description

A.Juss., Euphorb. Gen.: 50, t. 16, fig. 53. 1824 (‘Omalanthus’); Baill., Étude Euphorb.: 537; Atlas pl. 8, fig. 22–31. 1858; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.v: 42. 1912; Airy Shaw, Kew Bull. 26: 281. 1971; G.L.Webster, Taxon 24: 600. 1975; Ann. Missouri Bot. Gard. 81: 120. 1994; Esser, Blumea 42: 427. 1997; Radcl.-Sm., Gen. Euphorbiacearum: 354. 2001; Esser & Welzen in Welzen & Chayam., Fl. Thailand 8, 2: 334. 2007; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11: 196. 2014.— Carumbium Reinw., Syll. Pl. Ratisb. 2: 6. 1825.— Wartmannia Müll.Arg., Linnaea 34: 218. 1865.— Dibrachion Regel, Index Sem. Hort. Bot. Petrop. 1865: 51. 1866.— Carumbium Reinw. sect. Eucarumbium Müll.Arg. in DC., Prodr. 15, 2: 1143. 1866, nom. inval.

Trees, monoecious. Latex white, sticky. Indumentum of simple hairs, absent in most species. Stipules remarkably large, late caducous. Leaves alternate, simple; petiole glandless (Thailand); blade symmetric, base cuneate to emarginate, not to distinctly peltate, margin entire, adaxially glandless or with various glands, abaxially always with various glands; venation pinnate, nerves in 8–15 pairs below the apex, looped and joined, veins scalariform, veinlets more reticulate. Inflorescences axillary, thyrsoid, unbranched, bisexual, basal nodes with single pistillate flowers, distal nodes with cymules of 1–8 staminate flowers. Bracts of staminate cymules with one to several pairs of glands. Staminate flowers inclinate in bud, pedicellate; calyx with 1 or 2 kidney-shaped lobes; corolla, disc, and nectaries absent; stamens 4–30, free; pistillode absent. Pistillate flowers pedicellate; calyx persistent to caducous, consisting of 1–3 kidney-shaped lobes; corolla, disc, and staminodes absent; ovary 2- or 3-locular, each locule with 1 ovule. Fruit a woody capsule, primarily loculicidal, pericarp thick and then opening regularly, or pericarp thin and then opening tardily to irregularly. Seeds apically or completely covered by a thin arillode.

    Circa. 22 species ranging from S. Peninsular Thailand and Taiwan (Orchid Island) throughout Malesia to Australia, New Zealand and the W. Pacific. One species in Thailand. Classification: Subfam. Euphorbioideae, tribe Hippomaneae, subtribe Carumbiinae.

Homalanthus populneus (Geiseler) Pax in Engl. & Prantl, Nat. Pflanzenfam. 3.5: 96, excl. fig. 60. 1890; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.v: 46. 1912; Airy Shaw, Kew Bull. 26: 281. 1972; Whitmore, Tree Fl. Mal. 2: 102. 1973; Esser, Blumea 42: 453, map 9. 1997; Esser & Welzen in Welzen & Chayam., Fl. Thailand 8, 2: 334, Fig. 7. 2007.— Stillingia populnea Geiseler, Croton. Monogr.: 80. 1807.— Carumbium populifolium Reinw., Elench. Sem. Hort. Leiden ex Isis 1: 319. 1823.— Homalanthus leschenaultianus A.Juss., Euphorb. Gen.: t. 16 fig. 5.1824.— Excoecaria laevis Blanco, Fl. Filip.: 788. 1837 — Carumbium populneum (Geiseler) Müll.Arg. in DC., Prod. 15, 2: 1144. 1866.— Homalanthus populneus (Geiseler) Pax var. laevis (Blanco) Merr., Sp. Blancoan.: 230. 1918.— Homalanthus sulawesianus Airy Shaw, Kew Bull. 35: 398. 1980.

Trees up to 10 m tall; glabrous. Stipules 0.8–2 cm long. Leaves: petiole 1–15 cm long, glandless; lamina broadly ovate to deltoid, 3–22 by 1.5–20 cm, index 0.8–4.6, base rounded to slightly emarginate, not or indistinctly (up to 1 mm) peltate, with 2 or a single confluent gland (Thailand) above, apex acuminate, abaxially usually with 1–3 submarginal small glands on each side; nerves 9–15 pairs below the apex. Inflorescences 3–30 cm long. Bracts of staminate cymules c. 0.75–1.5 mm long, with a pair of large undivided glands. Staminate flowers: pedicel 0.6–3 mm long; sepals 2, c. 0.6 mm long; stamens (6–)8–10, filaments c. 0.4 mm long, anthers c. 0.3 mm long. Pistillate flowers: pedicel 3–12 mm long; sepals 2, soon caducous; ovary c. 2 mm long, 2-locular, style 0.6–1.5 mm long, stigma 1.5–3(–6) by 0.6–0.7 mm. Fruits: pedicel 1–2.5 cm long; fruit excl. style 4–9 by 5–8 mm, papillate, usually regularly loculicidal. Seeds 3.5–6 by 3–4 mm, upper half enveloped by an arillode.

    T h a i l a n d.— PENINSULAR: Pattani (Sai Khao Falls), Yala (Nikom Koa Long), Narathiwat (Bacho).

    D i s t r i b u t i o n.— Endemic to Malesia: S. Thailand, Malay Peninsula, Sumatra, Java, Borneo, Philippines (excl. N. Luzon), Celebes, Lesser Sunda Islands (W. part), Moluccas.

    E c o l o g y.— Usually in secondary vegetation, but also in cleared areas, plantations, road sides, steep slopes; locally common to gregarious and typical for the vegetation; on a large variety of soils: from shallow to thick, normal to ultramafic, poor to rich. Altitude: sea level up to 3,000 m. Ants' nests are commonly observed in the upper branches.

    V e r n a c u l a r.— Mae mae (แมแหมะ) (Narathiwat).

    U s e s.— The fruits are used medicinally for wounds, e.g., in Sabah. Leaves, dried on a fire, are used after birth by putting them on the stomach, or they are applied to the abdomen against fever by the Malay. Bark and leaves are, together with a certain kind of mud, used for dyeing cloths blackish. Dried and powdered leaves act as a vermifuge when fed to cattle; pounded leaves mixed with ashes and pepper act as fish poison. The wood is of low value and perishes quickly, but is good firewood. Sometimes planted, but only suitable for afforestation on better soils.