Bidens pilosa L.

• Title

  Bidens pilosa L.

• Authors

  Nathaniel Lord Britton, Frances W. Horne

• Scientific Name

  Bidens pilosa L.

• Description

  Flora Borinqueña Bidens pilosa Margarita Shepherd's-needle Family Garduaceae Thistle Family Bidens pilosa Linnaeus, Species Plantarum 832. 1753. Coreopsis leucantha Linnaeus, Species Plantarum, edition 2, 1282.1763. Bidens leucantha Willdenow, Species Plantarum 3: 1719. 1804. This herbaceous, annual weed, usually bearing conspicuous heads of white flowers, is common in fields, on banks, and in waste and cultivated grounds in Porto Rico; the plant is very widely distributed in tropical and warm temperate regions of America and of the Old World, ranging north to Bermuda and the southern continental United States. The original home of the species, prior to agriculture and commerce, is unknown; the fruits (schenes) are freely distributed by adhering to cloth, or other fabrics, or to the hair or fur of animals by the barbed awns of the pappus. While grouping it among the indigenous plants of Porto Rico, we have no evidence that it was not introduced. Romerillo is another Spanish name, referring to its wide distribution. For an account of the genus Bidens we refer to our description of Bidens reptans. Bidens pilosa (long-hairy, but the name is not well-applied) is upright, smooth, or somewhat hairy annual herb, from 0.3 to 1 meter high, and more or less branched. Its thin, slender-stalked leaves are 3-divided into ovate, or lance-shaped, pointed, toothed segments from 2 to 8 centimeters long, or the upper ones undivided and merely toothed. The bell-shaped involucre of the flower-heads is about 8 millimeters high, its outer bracts narrowly oblong, mostly shorter than the inner ones; the rays, usually, but not always developed, are white, 2-lobed, or 3-lobed, from 10 to 20 millimeters long. The slender schenes are unequal in length, the inner ones longer than the involucre; they bear a pappus of 2, 3 or 4 yellow, downwardly barbed awns.