Urena L.

Scientific Description

Common name. Burrs. Family Malvaceae.

Tribe Malvavisceae.

Habit and leaf form. Shrubs, or herbs (with a stellate indumentum). Plants unarmed. Annual, or perennial; to 0.5–2 m high. Mesophytic. Heterophyllous, or not heterophyllous. Leaves medium-sized; alternate; spiral; petiolate; non-sheathing; simple. Leaf blades dorsiventral; dissected (3–5-lobed), or entire; ovate, or orbicular; palmately veined; cordate, or rounded at the base (or truncate). Mature leaf blades adaxially pubescent; abaxially pubescent. Leaves with stipules. Stipules caducous, or persistent. Leaf blade margins crenate, or serrate. Leaf anatomy. Hairs present; complex hairs present. Complex hairs stellate. Extra-floral nectaries present (on the lower surface at the base of the main veins of the leaf).

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous.

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’ (due to the reduction of the upper leaves); axillary; in racemes. Inflorescences axillary; inflorescence of axillary, solitary or clustered flowers, sometimes apparently in short racemes. Flowers pedicellate (pedicels inarticulate); medium-sized; regular; 5 merous; tetracyclic. Hypogynous disk absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; lobed; lobulate (5-lobed), or toothed (5-toothed); valvate; exceeded by the corolla; campanulate, or tubular; regular. Calyx lobes ovate. Epicalyx present (campanulate to tubular and 5-lobed; the lobes alternate with those of the calyx; lobes narrowly oblong, linear or subulate). Corolla present; 5; 1 -whorled; polypetalous (tubiform, adnate to the base of the staminal column); hairy abaxially; glabrous adaxially; pink, or purple. Petals obovate. Androecium present. Androecial members indefinite in number. Androecium 50–100 (i.e. ‘many’). Androecial members adnate; all equal; coherent (connate; the filaments fused in a column surrounding the style); 1 - adelphous (the tube attached to the petals); 1 -whorled. Androecium exclusively of fertile stamens (or rather, half-stamens, each having only a half anther). Stamens 50–100. Anthers dehiscing via longitudinal slits; introrse; unilocular. Gynoecium 5 carpelled. The pistil 5 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary plurilocular; 5 locular. Gynoecium stylate. Styles 1; more than 4-branched (10-branched); apical. Stigmas 10; capitate. Placentation axile. Ovules 1 per locule.

Fruit and seed features. Fruit non-fleshy; a schizocarp (globular, dehiscing septicidally into indehiscent mericarps leaving a persistent central axis). Mericarps 5. Dispersal unit the mericarp (trigonous, dorsally convex and often glochidiate). Fruit 5 seeded (reniform in outline). Seeds 1 per locule; 1 per mericarp. Seeds small; conspicuously hairy, or not conspicuously hairy.

Geography, cytology, number of species. World distribution: pantropical. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, and Queensland. Northern Botanical Province. A genus of c. 6 species; 2 species in Western Australia; 0 endemic to Western Australia.