Spermacoce alata

Name and classification

Spermacoce alata Aublet
(=Borreria alata (Aublet) DC)
Family Rubiaceae

Common names

broadleaf buttonweed

Disseminule

seed

Description

Elliptic to oblong in outline, 1.5–3.0 mm long, 1.0–1.7 mm wide, 0.7–1.1 mm thick, revolute, with longitudinal cavity on ventral side. Longitudinal ridge inside cavity stringy, granular. Testa light to dark brown, dull to somewhat lustrous, shallowly pitted or pebbled; cavity and ridge straw-colored. Hilum inconspicuous. Embryo spatulate, cotyledons slightly expanded; endosperm present.

Identification considerations

As in Spermacoce and Borreria, seeds of some other genera in the Rubiaceae have a convex dorsal side and a flat side with a longitudinal slit, groove, or cavity.

Similar species

Borreria laevis (Lam.) Griseb. (non-FNW)

Distribution

Africa: Northwest Africa (southern coast), Uganda, and South Africa; Asia: southeast Asia and Iraq; Europe: Portugal, United Kingdom; Oceania: Australia, Fiji, Polynesia; South America: Brazil, French Guiana, Guyana, Suriname, Venezuela; North America: Costa Rica, Mexico, Lesser Antilles.

native to South America

Habitat

humid tropics, prefers sandy soils; steep riverbanks; a weed of fields, roadsides, disturbed sites

General information

Spermacoce alata is a prostrate or erect annual herb, up to 100 cm long, with an extensive root system. It is a weed of of cultivated crops such as sugarcane and soybeans, and plantation crops such as rubber. Its spread has accelerated in the last 20 years. It grows from seeds or cuttings.

dorsal view of seeds

dorsal view of seeds

ventral view of seeds

ventral view of seeds

side view of seed

side view of seed

surface detail of seed

surface detail of seed

A, fruit; B, seed; C, longitudinal section of seed showing embryo; D, transection of seed; drawing by Lynda E. Chandler

A, fruit; B, seed; C, longitudinal section of seed showing embryo; D, transection of seed; drawing by Lynda E. Chandler