Flora of Thailand Euphorbiaceae

The website deviates from the Flora of Thailand (based on Yu et al., Taxon 68, 2019, 918–936), where Tritaxis is still treated as Dimorphocalyx.

86. Tritaxis

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Genus description

Identification key

Species descriptions

Tritaxis

Baill., Étude Euphorb. (1858) 342; Benth. in Benth. & Hook.f., Gen. Pl. 3 (1880) 292; Pax in Engl., Planzenr. IV.147 (1910) 113; R.Y.Yu, Slik & Welzen, Taxon 68 (2019) 932.— Dimorphocalyx Thwaites, Enum. Pl. Zeyl. 278. 1861; Hook.f., Fl. Brit. Ind. 5: 403. 1887; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii: 31. 1911; Airy Shaw, Kew Bull. 26: 251. 1972; Whitmore, Tree Fl. Malaya 2: 86. 1973; Brandis, Ind. Trees: 581. 1978; Airy Shaw, Kew Bull. 35: 624. 1980; Kew Bull. 36: 286. 1981; G.L.Webster, Ann. Missouri Bot. Gard. 81: 106. 1994; Philcox in Dassan., Fl. Ceyl. 11: 107. 1997; Radcl.-Sm., Gen. Euphorbiacearum: 300. 2001; Phattar. & Chayam. in Chayam. & Welzen, Fl. Thailand 8, 1: 229. 2005; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11: 174. 2014.— Trigonostemon Blume sect. Tritraxis (Baill.) Müll.Arg., Linnaea 34 (1865) 213; in DC., Prodr. 15, 2 (1866) 1107.

Tree or shrub, dioecious (or monoecious); bark smooth; latex absent.  Indumentum simple hairs on new parts and flowers. Stipules triangular, short, caducous. Leaves alternate, simple, petiolate; blade coriaceous, margin entire to serrate, with or without glands beneath.  Inflorescences axillary to terminal, unisexual, with a single to few flowers in cymes, corymbs or racemes.  Flowers symmetric, pedicellate; calyx 5-lobed, imbricate; petals 5, white. Staminate flowers: sepals cup-shaped; disc glands 5, alternipetalous; petals longer than sepals; stamens 10–22 in 2 whorls, outer free, inner united, anthers with 2 thecae; pistillode absent. Pistillate flowers: sepals chataceous, in some species accrescent in fruit; petals shorter than calyx lobes when accrescent, membranous; disc annular; ovary 3-locular; ovules 1 per locule; style absent to short, stigmas stout, appically bifid.  Fruits capsular, 3-lobed, septicidally dehiscent into 2-valved cocci; columella subcapitate, persistent.  Seeds brown; ecarunculate.

    Twelve species in tropical Asia, ranging from India and Sri Lanka to Hainan, the Philippines, Moluccas, and Lesser Sunda Islands, one species up to Australia.  In Thailand 2 species.  Classification: Subfam. Crotonoideae, tribe Codiaeae.

Key to the species

1. Tritaxis malayana (Hook.f.) R.Y.Yu & Welzen in R.Y.Yu et al., Taxon 68 (2019) 933.— Dimorphocalyx malayanus Hook.f., Fl. Brit. Ind. 5: 404. 1887; Whitmore, Fl. Malay Pen. 2: 86. 1973; Phattar. & Chayam. in Chayam. & Welzen, Fl. Thailand 8, 1: 229, fig. 50. 2005.— Dimorphocalyx luzoniensis Merr., Philipp. J. Sc. 5, Bot. (1910) 192..— Dimorphocalyx kunstleri King ex Hook.f., Fl. Brit. Ind. 5: 405. 1887; Ridl., Fl. Mal. Pen. 2: 266. 1924.— Dimorphocalyx beccarii Gagnep., Bull. Soc. Bot. France 71: 621. 1924.— Trigonostemon bulusanensis Elmer, Leafl. Philipp. Bot. 10 (1939) 3735.—  Dimorphocalyx bulusanensis (Elmer) Airy Shaw, Kew Bull. 27 (1972) 92.

Shrub or tree 5–7 m high; bark smooth, white-grey.  Stipules triangular, c. 1 by 1 mm.  Leaves: petiole 0.8–1 cm long; blade o usually elliptic, 8.5-13 by 2.5–4.5 cm, glabrous, base cuneate, margin entire, with glands beneath, apex acute, nerves 8–10 pairs, midrib prominent on both sides.  Staminate inflorescences cymes or corymbs, (2–)3–7(–10.5) cm long, pedunculate; pistillate inflorescences simple flowered or corymbs, 1–2 cm long. Staminate flowers 3–5 mm in diameter; pedicel 8–12 mm long; sepals connate at base, oblong, c. 2.5 by 1 mm; petals oblong, c. 6 by 3 mm; stamens 11 or 12, outer free (to united), inner united, filaments 2–3 mm long, anthers oblong, c. 0.6 x 0.5 mm, yellow. Pistillate flowers: pedicels 1–1.6 cm long, sepals oblong to obovate, 5–10 by 4–6 mm, accrescent in fruit up to 8–17 by 5–8 mm, apex obtuse, green; petals oblong, c. 5 by 3 mm, membranous, glabrous; ovary subglobose, ca. 2 mm in diameter, glabrous; style stout, rigid dark brown, c. 2 mm long.  Fruit c. 10 by 6–7 mm, glabrous.  Seeds ovoid, c. 5 by 3 mm.

    T h a i l a n d.— PENINSULAR: Songkhla (Ton-Nga-Chang), Narathiwat (Bajo, Khao Tan Yong).

    D i s t r i b u t i o n.— India, Thailand, Malay Peninsula (type), Borneo.

    E c o l o g y.— Common on slopes in evergreen forest. Altitude: 50–200 m.  Flowering: March–May; fruiting: June–August.

    V e r n a c u l a r.— Khem yai (เข็มใหญ่) (Songkhla).

2. Tritaxis muricata (Hook.f.) R.Y.Yu & Welzen in R.Y.Yu et al., Taxon 68 (2019) 933.— Ostodes muricatus Hook.f., Fl. Brit. Ind. 5: 401. 1887.— Ostodes muricata Hook.f. var. ? minor Hook.f., Fl. Brit. Ind. 5 (1887) 401.— Trigonostemon asahanensis Croizat, J. Arnold Arbor. 23: 54. 1942. — Dimorphocalyx muricatus (Hook.f.) Airy Shaw, Kew Bull. 20: 412. 1966; Kew Bull. 26: 252. 1972; Whitmore, Tree Fl. Malaya 2: 87. 1973; Airy Shaw, Kew Bull. 36: 286. 1981; Kew Bull. 37: 16. 1982; Kew Bull. Add. Ser. 4: 97. 1975; Phattar. & Chayam. in Chayam. & Welzen, Fl. Thailand 8, 1: 231, fig. 51, plate XIII: 1. 2005.— Dimorphocalyx muricatus (Hook.f.) Airy Shaw var. minor (Hook.f.) Airy Shaw, Kew Bull. 20: 412. 1966.

Tree up to 10 m high; bark rather smooth, pale grey.  Stipules triangular, ca. 4 by 3 mm.  Leaves: petiole 3.5 cm long; blade (ovately) elliptic, 20–24 by 8–10 cm, chartaceous, glabrous, base cuneate, margin serrulate with gland in each tooth, apex acute or acuminate; nerves 10–12 pairs, midrib prominent on both sides.  Inflorescences corymbs; staminate ones up to 10 cm long; pistillate ones up to 8 cm long. Staminate flowers 1–1.5 cm in diameter; pedicel 0.8–1 cm long; sepals cup-shape, ca. 1 by 0.2 cm, pubescent outside; petals oblong, c. 8 by 3 mm, glabrous; stamens 14–22, filaments 2–5 mm long, partly united; anthers c. 1 by 0.8 mm. Pistillate flowers 1–1.2 cm in diameter; pedicels 0.7–1 cm long; sepals basally connate, oblong, c. 3 x 2 mm, pubescent outside, not accrescent in fruit; petals oblong, c. 4 by 3 mm, glabrous; ovary subglobose to ovoid, c. 3.5 by 2—3 mm, muricate; style stout, 2.5–3 mm long.  Fruits subglobose, 2.5–2.8 cm in diameter, muricate.  Seeds obovoid, c. 8 by 5 mm.

Fruits subglobose, 2.5–2.8 cm diam., covered with muricate

    T h a i l a n d.— PENINSULAR: Narathiwat (Waeng).

    D i s t r i b u t i o n.— Peninsular Thailand, Malay Peninsula incl. Singapore (type), Sumatra, Borneo, Moluccas.

     l = T. muricata («= T. ixoroides)

    E c o l o g y.— Scattered in evergreen forest up to 500 m.

    V e r n a c u l a r.— Mu yo ni ka (มูโย๊ะนีกา) (Malay-Narathiwat).