Parthenium hysterophorus L.

  • Authority

    Acevedo-Rodríguez, Pedro & collaborators. 1996. Flora of St. John, U.S. Virgin Islands. Mem. New York Bot. Gard. 78: 1-581.

  • Family

    Asteraceae

  • Scientific Name

    Parthenium hysterophorus L.

  • Description

    Species Description - Erect annual herb 30-75 cm tall; stems much-branched, strigose and often scabrous throughout, conspicuously striate at least on younger parts. Leaves sessile above or lower ones with a winged petiole; upper stem leaves much reduced, lanceolate in outline, lower stem leaves with blades to 20 x 12 cm, ovate to oblong in outline, pinnatifid or bipinnatifid, the segments 2-6, paired, to 7 x 3 cm, linear or lanceolate, dentate or lobate. Inflorescence paniculate, with many small heads. Heads radiate; involucral bracts biseriate, the outer involucral bracts 5, separate, narrowly ovate, 1.5-2 mm long, acute, palea elliptic, ca. 1 mm long. Ray flowers inconspicuous; corollas cream-colored, persistent on achenes, the limb ca. 0.5 mm long, the tube obscure. Disk flowers many; corollas light yellow, ca. 1-2 mm long; ovary sterile; some outer flowers functionally male. Achenes flattened, 2 mm long; pappus of 2 broad awns 0.5 mm long; achenes falling in a complex of 1 ray achene (and the persistent corolla) and its subtending involucral bract and 2 disk flowers with their palea.

  • Discussion

    Common names: false ragweed, feverfew, mule weed, quinine weed, whitehead broom.

  • Distribution

    Common in waste or open disturbed areas. Enighed (A3930). Also on St. Croix, St. Thomas, and Tortola; throughout much of the West Indies, primarily Mexican, but ranging from the southern United States into Central America, South America, and the paleotropic.

    Saint Croix Virgin Islands of the United States South America| Saint Thomas Virgin Islands of the United States South America| Tortola Virgin Islands South America| West Indies| Central America| South America|