Sida acuta Burm.f.

Burman, N.L. (1768) Flora Indica : 147. Type: Habitat in India.

Sida; Sida, Spinyhead; Southern Sida; Spinyhead Sida; Sida, Southern

Usually flowers and fruits as a shrub about 1-1.5 m tall, occasionally flowers when smaller.

Leaf blades about 4 x 0.8 cm, margin coarsely serrate, each tooth ending in a single hair. Stipules in each pair differing from one another, one stipule linear to lanceolate and 3-6 veined about 8 x 0.5 mm; the other stipule linear to filiform, shorter and 1-4 veined. Stellate hairs present on the twigs and petioles. Stem and twig bark strong and fibrous when stripped.

Calyx 10-ribbed, at least towards the base, about 6-8 mm long, outer surface clothed in stellate hairs. Petals about 7-8 mm long, attached to the base of the staminal column and falling off with it. Stamens about 30, arranged in five bundles of 6. Ovary about 5-10 locular. Styles and/or stigmas protrude from among the mass of anthers.

Calyx persistent, nutlets about 6-10, each about 2-2.5 mm long with two awns, each about 1-1.5 mm long at the apex. Seeds ovoid, about 2 mm long, mainly glabrous.

Cotyledons almost orbicular, about 6 mm diam., apex shortly apiculate, petioles about 3 mm long. First pair of leaves +/- obovate, margins toothed, lower surface clothed in stellate hairs, upper surface clothed in simple hairs. At the tenth leaf stage: leaf blade ovate, apex acuminate, base cuneate. Stipules hairy, filiform, about 9-11 mm long, one stipule in each pair wider than the other. Stem bark very fibrous when stripped. Seed germination time 21 to 77 days.

An introduced species with a pantropic distribution, now naturalised in NT, CYP, NEQ and CEQ. Altitudinal range in northern Australia from near sea level to 500 m. Usually grows as a weed of agricultural land and waste places but also found in disturbed areas and along roads in rain forest.

This species may have medicinal properties.