Spermacoce alata Aublet(=Borreria alata (Aublet) DC)
Common names: broadleaf buttonweed
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.
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.
Borreria laevis (Lam.) Griseb.
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.
Humid tropics, prefers sandy soils; steep riverbanks; a weed of fields, roadsides, disturbed sites.
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.