Commelinaceae — Spiderwort Family
This annual herbaceous plant has sprawling, hairy stems to 15 inches long. The leaves are alternate, with ovate blades about twice as long as wide, 1 to 4 inches long, and as much as 2 inches wide, and sparsely hairy on both surfaces. The petiole base forms a sheath around the stem, the upper margin with reddish brown (or sometimes pale tan), eyelash-like hairs. The flowers appear from a modified, folded leaf called a spathe, about a half-inch across, with two conspicuous blue or purple petals and a third smaller, inconspicuous, white or pale blue petal. In addition, closed, white, self-pollinating (cleistogamous) flowers are borne on underground stolons (a creeping horizontal plant stem, also called a “runner”). The small brown seeds are produced by both above-ground and below-ground flowers.
The plant is native in the Old World tropics and subtropics, but has spread to the United States, the West Indies and South America. In this country, it has been reported in Alabama, California, Florida, Georgia, Louisiana, Mississippi and North Carolina.
This weed grows in cultivated fields, nursery beds and containers, lawns and other disturbed areas in scattered counties from the Panhandle nearly to Lake Okeechobee in the central part of the state. It will undoubtedly spread to other areas in the future.
Seven other species of Commelina occur in the state, and only two of these are native. None of the others produce underground stolons with cleistogamous flowers. The broad leaves of this species (usually about twice as long as broad) with a dull texture, and the brown-tipped, eyelash-like hairs on the petiole and sheath are also distinctive. Plants of the completely unrelated genus Richardia, the Mexican clovers in the madder family (Rubiaceae), are often mistaken for the Benghal dayflower, but they differ significantly in their opposite leaves and white or pink, usually six-parted, flowers in dense heads.
The sprawling stems produce roots at the nodes, and detached pieces can grow into new plants. But the profusely borne seeds, from both the above-ground and below-ground flowers, are the primary means of reproduction and dispersal.
This is usually an annual plant, and new seedlings start to appear in April or May in northern Florida. In warmer climates, it may be perennial. It is a serious problem in fields of peanuts, soybeans and cotton because it is resistant to most commercial herbicides. Manual eradication is also difficult because of its habit of rooting at the nodes. It has been established in Florida since at least 1935, but only within the last two decades has it become a serious problem. It is listed as a noxious weed by the United States Department of Agriculture, as well as by the state of Florida (Rule 5B-57.007 F.A.C.).