Flora of the Hawaiian Islands
Dicotyledon Literature for Parthenium hysterophorus
Wagner et al., 1990, 1999; Lorence & Wagner, 2020.
   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.
















Habit
Taprooted, annual herb, 3‒10 dm tall; stem unbranched in proximal part, branched in distal part, longitudinally striate, hirsute.
Leaves
Proximal leaves in a basal rosette, these deciduous at maturity and stem leaves remaining, short-petiolate; blade 3‒20 cm long, 2‒10 cm wide, bipinnatifid or pinnatifid.
Flowers
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.
Fruit
Achenes black, obovate, 2‒2.5 mm long.
Chromosomes
2n = 18, 34 36.
Contributor
Nancy Khan