Malesian Euphorbiaceae Descriptions

107. WETRIA (Euphorbiaceae)

P.C. van Welzen

Welzen, P.C.  van. 1998. Revisions and phylogenies of Malesian Euphorbiaceae: Subtribe Lasiococcinae (Homonoia, Lasiococca, Spathiostemon) and Clonostylis, Ricinus, and Wetria. Blumea 43: 131–164.

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Genus description

Key to the species

Species descriptions

Wetria Baill.

    Wetria Baill., Étude Euphorb. (1858) 409; J.J.Sm. in Koord. & Valeton, Meded. Dept. Landb. Ned.-Indië 10 (1910) 470; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 219; Backer & Bakh.f., Fl. Java 1 (1963) 485; Airy Shaw, Kew Bull. 26 (1972) 350; Whitmore, Tree Fl. Malaya 2 (1973) 136; Airy Shaw, Kew Bull. Add. Ser. 4 (1975) 206; Kew Bull. Add. Ser. 8 (1980) 206; Kew Bull. 36 (1981) 358; Alph. Enum. Euph. Philip. Isl. (1983) 48; G.L.Webster, Ann. Missouri Bot. Gard. 81 (1994) 86; Welzen, Blumea 43 (1998) 156; Radcl.-Sm., Gen. Euphorbiacearum (2001) 209, fig. 27; Welzen in Welzen & Chayam., Fl. Thailand 8, 2 (2007) 590; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11 (2014) 117, Fig. 26. — Type: Wetria trewioides Baill. [= Wetria insignis (Steud.) Airy Shaw]

    Pseudotrewia Miq., Fl. Ind. Bat. 1, 2 (1859) 414, nom. illeg. (see note). — Type: Pseudotrewia macrophylla (Blume) Miq. [= Wetria insignis (Steud.) Airy Shaw]

Trees, dioecious; flowering twigs smooth, lenticellate, glabrous except when young. Indumentum existing of simple hairs only. Stipules falcately triangular, parallel nerved, asymmetric, mainly one side developed, glabrous to outside hairy, early caducous. Leaves spirally arranged, simple; petiole short, flattened above, basally to completely pulvinate; blade somewhat obovate, papery, symmetric, base cuneate, margin (indistinctly) serrate with a gland in each tooth, apex tapering acuminate to cuspidate, very apex often mucronulate, upper surface smooth, glabrous with especially basally glands, lower surface smooth, glabrous to subhirsute, with especially subapically glands, glands few to many, round, black, more ore less in line with each other, venation especially raised on lower side, nerves looped and joined near margin, veins scalariform, veinlets laxly reticulate. Inflorescences mainly axillary and single to ramiflorous and in small groups, unbranched racemes, pendulous, flattened, subhirsute, green, staminate ones with groups of 2–4 flowers per node, pistillate ones with single flowers per node. Bracts and bracteoles ovate, glabrous except for pilose margin. Flowers actinomorphic, sepals valvate, reflexed, petals and disc absent, pedicellate with a subbasal abscission zone. Staminate flowers: sepals (2) 3 (4), ovate, glabrous except for some apical hairs; stamens 16–26, filaments glabrous, often adnate because of mucilage; anthers 4-locular, basifixed, opening introrse with lengthwise slits, connective appendaged or not; pistillode absent. Pistillate flowers: pedicel elongating in fruit; sepals 5, ovate, margin pilose, apex tapering; pistil 3 (4)-locular, one ovule per locule, ovary smooth, tomentose; style densely hirsute, stigmas 3 (4), split, hirsute below, above papillate. Fruits lobed capsules, smooth, outside tomentose, inside glabrous, woody, thin-walled, septicidally breaking into 3 bivalved parts; column after dehiscence with a narrow frayed septum margin and a broadened apex, obtriangular in longitudinal section, with 2 extensions per septum; septa with 2 vascular bundles. Seeds usually 2 or 3 per fruit, globular; caruncle or arilloid absent; embryo basally covered by endosperm, latter with frayed margin.

    Distribution — Two species, one ranging from Peninsular SE Asia (Myanmar, Thailand) to W Malesia (up to Philippines, Borneo, Lesser Sunda Islands), the other in Papua New Guinea and NE Australia.

    Note — The name Pseudotrewia Miq. is an illegitimate, superfluous name, because the type species refers to the same type specimen as the type species of Wetria.

Key to the species

1. Wetria australiensis P.I.Forst. 

    Wetria australiensis P.I.Forst., Austrobaileya 4 (1994) 141; Welzen, Blumea 43 (1998) 157, fig.5, i, j; Map 4. — Type: C. Lyons 105 (BRI, holo, n.v.), Australia, Queensland, Cook District, Cairns, Currunda Creek.

    Wetria insignis auct. non Airy Shaw: Airy Shaw, Kew Bull. 27 (1972) 87; Kew Bull. Add. Ser. 8 (1980) 207.

Tree, up to 15 m high; flowering twigs c. 4 mm thick. Bark black and white blotched or grey-brown, smooth; inner bark light brown, thin; wood straw. Stipules 0.3–1.1 cm by 1.5–2 mm, outside partly hairy. Leaves: petiole 0.4–1 cm long; blade 8-30 by 5–10 cm, ratio 1.6–3.1, pale reddish green when young, medium green when mature, glands more or less in line at c. 1/3 from midrib, nerves 14–18 pairs. Inflorescences: staminate ones up to 15 cm long, pistillate ones up to 28 cm long. Bracts 0.9–1.5 by 0.9–1 mm, bracteoles c. 0.3 by 0.2 mm. Flower buds of staminate flowers reddish brown. Staminate flowers c. 4.7 mm in diam.; pedicel 0.1–1 mm long, subglabrous; sepals 2-3 by 1.5–3 mm; stamens: filaments 1–1.7 mm long, anthers 0.5–1 by 0.7–1 mm, connective with an apical appendage of 0.5–0.7 mm long. Pistillate flowers c. 3 mm in diam.; pedicel up to 3.5 mm long, hirsute; sepals 1.5–2.8 by 1–1.2 mm; ovary 1–1.1 by 1–1.4 mm in diam.; style absent or perhaps up to 0.2 mm long; stigmas 3, 3–5 mm long, split after 1–1.5 mm. Fruits 9–10 by 4–6 mm. Seeds 4–5 mm in diam.; embryo not seen.

    Distribution — E Malesia (Papua New Guinea: Central and E Sepik Prov.) and NE Australia (Queensland: Cook Distr.).

(squares in New Guinea and Australia)

    Habitat & Ecology — Common in primary and secondary forest, riverine forest, Australian complex notophyll vine forest, along rivers, and margin of forest. Soil: limestone, reddish soil, metamorphics. Altitude: 50–270 m. Flowering: February, October, December; fruiting: January.

2. Wetria insignis (Steud.) Airy Shaw 

    Wetria insignis (Steud.) Airy Shaw, Kew Bull. 26 (1972) 350; Whitmore, Tree Fl. Malaya 2 (1973) 136; Airy Shaw, Kew Bull. Add. Ser. 4 (1975) 206; Kew Bull. 36 (1981) 358; Alph. Enum. Euph. Philip. Isl. (1983) 48; Welzen, Blumea 43 (1998) 157, fig 5a–h, Map 4; in Welzen & Chayam., Fl. Thailand 8, 2 (2007) 591, Fig. 98, Plate XXXII: 3. — Trewia macrophylla Blume, Bijdr. (1825) 612; nom inval., non Roth, Nov. Pl. Sp. (1821) 373 (= Trewia nudiflora L.). — Trewia insignis Steud., Nomencl. Bot. ed. 2, 2 (1841) 698, nom. nov. — Wetria trewioides Baill., Étude Euphorb. (1858) 409, nom. superfl.; Ridl., Fl. Malay Penins. 3 (1924) 282. — Pseudotrewia macrophylla (Blume) Miq., Fl. Ind. Bat. 1, 2 (1859) 414, nom. illeg. — Alchornea blumeana Müll.Arg., Linnaea 34 (1865) 167, nom. superfl.; in DC., Prodr. 15.2 (1866) 900. — Wetria macrophylla (Blume) J.J.Sm. in Koord. & Valeton, Meded. Dept. Landb. Ned.-Indië 10 (1910) 471, nom. illeg.; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 219; Merr., J. Straits Branch Roy. Asiat. Soc., Spec. no. (1921) 341; Enum. Philipp. Fl. Pl. (1923) 437; Philipp. J. Sci. 24 (1924) 115; Philipp. J. Sci. 29 (1926) 383; Airy Shaw, Kew Bull. 14 (1960) 473; Kew Bull. 16 (1963) 383; Backer & Bakh.f., Fl. Java 1 (1963) 485. — Lectotype (designated by Welzen, 1998): Blume (Anonymous) ‘1521’ (L, holo, barcode L 0026857; iso in K), Indonesia, Java. (see note).

    Agrostistachys pubescens Merr., Philipp. J. Sci. C. Bot. 4 (1909) 274; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vi (1912) 99. — Type: FB (Curran) 5940 (PNH, holo, †; iso in K), Philippines, Luzon, Butaan Prov., Mabayo.

    Trigonostemon forbesii Pax in Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 88; Jabl., Brittonia 15 (1963) 165. — Type: Forbes 1892 (iso in L), Indonesia, Sumatra, Lampong, Mt. Tengamoes (= Gunung Tanggamus).

Tree, up to 27 m high, d.b.h. up to 45 cm; buttresses absent; flowering twigs 4–15 mm thick. Bark gray, white and gray spotted, (light brown, brown-green, dark green), smooth (to scaly), 0.5–1 mm thick; inner bark yellowish, pale yellow-brown, light brown, yellow-orange, 3-5 mm thick, fibrous, laminated; cambium brown, red, white-greyish; sapwood white, medium soft. Stipules 0.6–1.2 cm by 2.6–4 mm, glabrous. Leaves: petiole 0.6–1.5 cm long; blade 9.5–56 by 4–21.5 cm, ratio 2.6–3.2, red when young, glands more or less in line at c. 1/3 from margin, nerves 19–32 pairs. Inflorescences: staminate ones up to 42 cm long, pistillate ones up to 90 cm long. Bracts 1–1.8 by 1.2–1.8 mm, bracteoles 0.4–0.9 by 0.4–0.7 mm. Flower buds brown-green. Staminate flowers white or creamy, 5–5.5 mm in diam.; pedicel 2.6–8 mm long, (sub)hirsute; sepals 2.8–3.1 by 1.3–3.2 mm; stamens: filaments creamy white, 2.8–3 mm long, anthers 0.8–1.2 by 0.7–1 mm, connective without or with very short apical appendage less than 0.2 mm long. Pistillate flowers green to green-yellowish, 2.8–4.8 mm in diam.; pedicel up to 10 mm long, hirsute; sepals 1.5–3.2 by 0.3–2 mm; ovary 2.6–4.6 mm in diam.; style 0.2–2 mm long; stigmas 3 (4), 5.8–13 mm long, split after 0.1–3 mm. Fruits 1.3–1.7 by 0.6–1 cm, outside creamy white to grey tomentose, green to yellow-green when immature. Seeds 6–9 mm in diam.; embryo c. 8 by 7 by 6 mm.

    Distribution — Ranging from Southeast Asia mainland (Myanmar, Thailand) to W Malesia (Sumatra, Java, Lesser Sunda Islands, Borneo, Philippines).

(dots in West Malesia)

    Habitat & Ecology — Often common in understorey of primary and secondary mixed Dipterocarp forest, Thai evergreen forest, riverine forest, logged over forest, seldom also in cultivated forest; on ridges, steep slopes, level ground, and along rivers. Soil: limestone, sandstone, sandy raised coral, loam, Tertiary granodiorite; usually lime present. Altitude: 5–650(–1830) m. Flowering and fruiting whole year through.

    Vernacular names — Sumatra: Benoewa, langsat hutan, medang tjempaka. Peninsular Malaysia: Nye-nyelong. Java: Ki-sempoer, ki-tjaloeng, pakilan (J.J.Sm. 1910). Borneo, Sabah: Bubal (Dusun Banggi); rambay utan (Malay; Merr. 1924). Philippines: Malatibig (Tagalog).

    Note — Blume created a later homonym when he described Trewia macrophylla. Later authors tried to correct this, but all those who used the same epithet in other genera created illegitimate names (Pseudotrewia macrophylla Miq., Wetria macrophylla J.J.Sm.). Steudel was the first to correct Blume’s mistake, all others who followed created superfluous names (Wetria trewioides Baill., Alchornea blumeana Müll.Arg.).