Cyathula prostrata (pasture weed)

Cyathula prostrata is an annual to short-lived perennial herb native to Africa and Asia and some parts of Oceania, now found naturalized elsewhere in Oceania and in South and Central America. It grows as a weed in cultivated land, roadsides, grazing land, along seashores and in primary and secondary forests and is classed as an invasive species in a number of Pacific Islands.

Cyathula is a genus in the Amaranthaceae that consists of about 25 species with a tropical distribution (Chuakul et al., 2001; World Flora Online, 2020). World Flora Online (2020) include two accepted varieties of C. prostrata: C. prostrata var. lancifolia and C. prostrata var. pedicellata.

The following description is from Chuakul et al. (2001):

An annual to perennial herb, 30-50 cm tall, erect or ascending, rooting at the nodes, stem obtusely quadrangular, thickened above the nodes, often tinged with red, covered with patent, fine hairs. Leaves opposite, simple, rhomboid-obovate to rhomboid-oblong, 1.3-15 cm × 0.7-6.5 cm, base contracted or narrowed, rounded, apex triangular, acute to obtuse, entire, ciliate, margin or blade often tinged red; petiole short. Inflorescence an erect, elongated raceme, terminal and in highest leaf-axils, straight or sinuous, 18-33 cm long, rachis densely pubescent; peduncle 1-12 cm long; flowers in small clusters, in the lower part of the raceme distant, in the higher part crowded, pedicel short, erect before anthesis, reflexed in fruiting, bracts ovate, acuminate; lower clusters with 2-3 bisexual flowers and several sterile ones, with up to 20 red, hooked awns, towards the apex fewer sterile flowers, at apex only solitary bisexual flowers, ripe clusters falling off as a whole. Flowers small; tepals 5, free, in bisexual flowers ovate-oblong, 2.5-3 mm long, strongly mucronate, dull pale green, glabrous within, externally clothed with patent long, white hairs, tepals of sterile flowers 1.7-2.5 mm long, sessile; stamens 5, filaments connate at base, free parts 1 mm long, anthers two-celled, pseudo-staminodes rectangular-cuneate, apex truncate; ovary superior, obovoid, one-celled, funicle short, style filiform, stigma capitellate. Fruit an ellipsoid utricle, 1.5-2 mm long, thin-walled, glabrous, one-seeded, surrounded by stiff perianth. Seed ovoid or ellipsoidal, 1-1.5 mm long, shiny brown. Seedling with epigeal germination.

Cyathula prostrata is native to Africa, Asia and Papua New Guinea, Palau, Timor-Leste and North-East Australia in Oceania. It now has a pantropical distribution after being introduced in other countries in Oceania and in Central and South America.

Cyathula prostrata has a weedy habit and is found in forests, plantations, rough pastures, along roadsides and in wet areas such as by swamps and streams (Adams, 1972; PROTA, 2015; Useful Tropical Plants, 2020)

Cyathula prostrata has been reported as a weed in cocoa and rubber plantations (PROTA, 2015)