Flora of the Hawaiian Islands
Dicotyledon Literature for Parthenium hysterophorus
Wagner et al. 1990, 1999..
   Asteraceae -- The Sunflower Family Bibliography
      Parthenium hysterophorus

Common name(s): false ragweed, Santa Maria (Spanish)
General Information
DistributionNative to tropical America.In the Hawaiian Islands, naturalized on Kaua`i, O`ahu, Moloka`i, Maui, Hawai`i.

Taprooted annual herbs 3-10 dm tall; stems unbranched in lower part, branched in upper part, longitudinally striate, hirsute.
Lower leaves in a basal rosette, these deciduous at maturity and stem leaves remaining, 3-20 cm long, 2-10 cm wide, bipinnatifid or pinnatifid.
Heads small, numerous in open panicles; rays white, 0.6 mm long; disk corollas cream colored, ca. 1 mm long; pappus of 2 petaloid scales inserted close to the corolla on either side, entire or notched.
Achenes black, obovate, 2-2.5 mm long.
2n = 18, 34 36.