Ageratum conyzoides L.

• Title

  Ageratum conyzoides L.

• Authors

  Nathaniel Lord Britton, Frances W. Horne

• Scientific Name

  Ageratum conyzoides L.

• Description

  Flora Borinqueña Ageratum conyzoides Yerba de cabrio Wild Ageratum Family Carduaceae Thistle Family Ageratum conyzoides Linnaeus, Species Plantarum 839. 1752. Common, often as a weed, nearly throughout all tropical and subtropical regions, this herbaceous plant, annual in duration, is plentiful in Porto Rico at lower and middle elevations, growing on banks, in fields and waste grounds; its small heads of white or blue flowers are not as attractive as those of the Garden Ageratum, Ageratum Houstonianum, native of Mexico, and grown for ornament. The Spanish popular name means Goat-weed in English. The plant is of American origin; we regard it as indigenous in Porto Rico, but it may have been introduced, long ago, from some other part of tropical America. Mentrasto is another recorded Spanish name. Ageratum is a genus established by Linnaeus in 1753, with the species here illustrated typical. The name is an ancient one, not originally applied to these plants. There are about 15 species, all but an African one natives of warm and tropical America. They are herbs or low shrubs, their leaves mostly opposite, their small, blue or white, tubular flowers in clustered heads. The involucre of the flower-heads is bell-shaped, or hemispheric, with 2 or 3 series of bracts, nearly alike. The corollas are 5-toothed. The fruits (achenes) are 5-angled, bearing a pappus of several scales. Ageratum conyzoides (like Conyza; a somewhat related genus) is a usually branched herb, from 0.4 to nearly 1 meter high, and more or less hairy. The thin, slender-stalked, mostly blunt leaves are ovate, from 2 to 8 centimeters long, their margins bluntly toothed. The flower-heads are about 6 millimeters broad, with a bell-shaped involucre of oblong, pointed bracts. The shining, black achenes are topped by from 1 to 5 pointed scales.