Malesian Euphorbiaceae Descriptions

84. PETALOSTIGMA (Picrodendraceae)


P.I. Forster & P.C. van Welzen


Forster, P.I. & van Welzen, P.C. 1999. The Malesian species of Choriceras, Fontainea, and Petalostigma (Euphorbiaceae). Blumea 44: 99–107.

van Welzen, P.C. & Forster, P.I. 2011. Picrodendraceae (formerly Euphorbiaceae s.l. subfam. Oldfieldioideae). In: Nooteboom, H.N. (ed.), Flora Malesiana ser. 1, 20: 45–61.


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Genus description

Species description


Petalostigma F.Muell.


    Petalostigma F.Muell., Hook. J. Bot. Kew Gard. Misc. 9 (1857) 16; Pax & K.Hoffm. in Engl., Pflanzenr. VI.147.xv (1922) 281; Airy Shaw, Kew Bull. 31 (1976) 366; Kew Bull. 35 (1980) 661; Kew Bull. Add. Ser. 8: (1980) 178; G.L.Webster, Ann. Missouri Bot. Gard. 81 (1994) 58; P.I.Forst. & Welzen, Blumea 44 (1999) 105; Radcl.-Sm., Gen. Euphorbiacearum (2001) 95; Welzen & P.I.Forst. in Noot., Fl. Males. ser. 1, 20 (2011) 59; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11 (2014) 97. —Type: Petalostigma quadriloculare F. Muell.


Shrubs or trees, evergreen, dioecious; stems and foliage without conspicuous latex. Bark greyish black, tesselated. Indumentum of simple hairs, not glandular, stinging hairs absent. Stipules entire, inconspicuous, caducous. Leaves alternate, simple, petiolate, elobate, penninerved, margin entire, glands absent. Inflorescences axillary, bracteate fascicles or very short racemes with groups of flowers. Flowers actinomorphic; petals absent; disc absent. Staminate flowers pedicellate; sepals 4, free, imbricate, cucullate, ± equal; petals absent; disc absent; stamens 18-86, filaments connate and attached to a slightly raised receptacle; anthers dorsifixed, bilobate, thecae oblong, longitudinally dehiscent; pistillode absent. Pistillate flowers sessile to pedicellate; sepals 6–8, imbricate, free; ovary 3- or 4-locular, ovules 2 per locule, style short, stigmas simple, flabellate (petal-like). Fruits capsular, quadri- or trilobate, tardilly dehiscing septicidally into bivalved cocci; sarcocarp fleshy, orange to red. Seeds ellipsoid to flattened ellipsoid to ovoid; testa crustaceous; albumen fleshy; caruncles entire, non-arilloid; cotyledons broad, flat.

    Distribution — Five species from Australia, one also in Malesia: New Guinea.

    Habitat & Ecology — Trees in open woodland and open forest dominated by Eucalypts. Alt.: 50–900 m. Flowering and fruiting after seasonal storm rains.


Petalostigma pubescens Domin 


    Petalostigma pubescens Domin, Biblioth. Bot. 89 (1928) 871; Airy Shaw, Kew Bull. 31 (1976) 368; Kew Bull. Add. Ser. 8 (1980) 178; Kew Bull. 35 (1980) 663; P.I.Forst. & Welzen, Blumea 44 (1999) 105, Fig. 3; Welzen & P.I.Forst. in Noot., Fl. Males. ser. 1, 20 (2011) 60, fig. 5. — Lectotype (designated by Airy Shaw, 1976): Mitchell 438 / 615, young fruiting specimen (K, holo), Australia, ‘Subtropical New Holland’ (Queensland, W of Brisbane).

    Petalostigma quadriloculare F.Muell. var. pubescens Mόll.Arg., Flora 47 (1864) 481. — Type: F. Mueller s.n., 1855-7 (K, holo), Australia, Northern Territory, Arnhem Land.

    Petalostigma quadriloculare F.Muell. var. genuina Mόll.Arg. in DC., Prodr. 15, 2 (1866) 273, nom. illig. — Type: F. Mueller s.n., 1855-7 (K, holo), Australia, Northern Territory, Arnhem Land.

    Petalostigma quadriloculare F.Muell. var. nigrum Ewart & O.B.Davies, Fl. Northern Territory (1917) 166, t. 17. — Syntypes: Campbell 17 (MEL), Australia, N of 15 degrees; G.F. Hill 387 (MEL), Australia, Northern Territory, 70 miles N of Camp IV; G.F. Hill 908 (MEL), Australia, Northern Territory, Borroloola.

    Petalostigma nummularium Airy Shaw, Kew Bull. 31 (1976) 373; Kew Bull. 35 (1980) 663. — Type: C.R. Dunlop 2290 (K, holo; iso in BRI, DNA), Australia, Northern Territory, W of Frewena

    Petalostigma australianum auct. non Baill.: Baill., Adansonia 7 (1867) 356, t. 2, pro parte (‘Crescit in Australia .... Leichhardt, t. 2), nom. superfl.


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Shrub to small tree up to 7 m high, usually single stemmed. Bark roughly fissured, black-grey. Indumentum of yellow-ferruginous simple hairs, mainly glabrescent. Leaves: stipules linear-lanceolate, 4–6 by 0.3–0.8 mm, with dense hairs; petioles 2.5–10 by 0.5–1 mm, densely hairy; lamina elliptic, orbicular or ovate, 10–65 by 7–45 mm, strongly discolorous, base cuneate, rounded or truncate, apex rounded to apiculate, upper surface dark glossy green, not granular, with sparse hairs when young, lower surface cream to cream-brown or ferruginous-brown, densely sericeous; venation comprising 5–7 pairs of nerves, veins ± obscure, reticulate. Flowers cream. Staminate flowers 4–5 by 5–12 mm diam.; pedicels 1–2 by 0.7–1 mm diam., with sparse hairs; sepals 4, orbicular, broadly-ovate to obovate, cucullate, 3.5–6 by 2.5–5 mm, sparsely hairy outside; stamens 28–68, connate into a column of 1.5–2 mm high; filaments 0.8–1.2 mm long, connate for most of their length, anthers oblong, 1.5–2 by 0.5–1 mm, usually with sparse hairs on apex of connective although occasionally glabrous. Pistillate flowers 5–10 by 5–8 mm diam.; pedicels 1.5–2.5 by 1–1.5 mm diam., densely hairy; sepals 8, ovate to lanceolate-ovate, 3.5–5.5 by 1.5–3 mm, densely hairy outside; ovary ovoid, 3.5–4 by c. 3 mm diam., with dense antrorse hairs; stigmas 4, lanceolate-oblong, 5–6.5 by 1.4–2.5 mm, with sparse hairs on top and densely hairy on back. Fruit globose to subglobose, 11–22 by 15–20 mm diam., orange-yellow to orange. Seed ellipsoid, 6–9 by 3–4.5 by 3–4 mm thick, smooth to slightly rugose, glossy red-brown; caruncle ± reniform, 1.5–2.5 by 1.8–2.5 mm, yellow to yellow-red.

    Distribution — Malesia: Papua New Guinea (Western Prov.); and N and E Australia (Western Australia, Northern Territory, Queensland, New South Wales).

    Habitat & Ecology — Open woodland and open forest dominated by eucalypts, also in coastal sand-dunes; on various soils. Altitude: 20–900 m.