Commelina benghalensis (COMMELINACEAE) Hairy Commelina, Tropical Spiderwort

Weeds to Whack

Hairy Commelina Commelina benghalensis is an annual or sometimes perennial herb, also known as Bengal Dayflower and Tropical Spiderwort. Stems have a high moisture content. Once well rooted the plant can survive for long periods without moisture availability and can then grow rapidly on the onset of rains. An aggressive weed that produces aerial (above ground) and subterranean (below ground) flowers. This results in viable seed being produced both above and below ground. Will also root at the nodes and can be propagated from cut stems. Tolerance to glyphosate has been documented. Light cultivation can often break plant parts and increase the area of infestation. Commelinaceae named for 17th century Dutch botanist Jan Commelin.
Photo: Robert Whyte

Brown Hairs, Hairy Fused Spathe

Confusion can occur with a number of other Commelina species, but the following combination of characters may be used to distinguish C. benghalensis – all three petals blue, leaves broadly elliptical (length up to twice width only), spathe sealed to form triangular pocket, seeds rugose, presence of stolons, leaf sheaths with reddish-brown-tipped hairs. Commelina diffusa, the commonest of other species, has blue petals, but the spathe is open along one edge, leaves are narrower, seeds are smooth, and there are no stolons. C. forskalaei has stolons and rough seeds, and the spathe is sealed, but the leaves are narrower, and their length is up to four times the width, and wavy-edged (Holm et al 1977, Drummond 1984). None of the other weedy species have brown-tipped hairs. Hence this is an especially useful character when looking at vegetative material. SOURCE: North American Plant Protection Organization (NAPPO)
Note brown-tipped hairs and fused hairy spathe. Photo: Robert Whyte