Other names: Ragweed, Parthenium ragweed, Santa Maria
Scientific name: Parthenium hysterophorus L.
Description: A warm-season annual commonly found in row-crop fields and roadsides throughout South Texas. Similar in appearance to the true ragweeds (genus Ambrosia). This species is naturally tolerant to paraquat (Gramoxone). Additionally, glyphosate (Roundup) resistant populations are common in the Lower Rio Grande Valley and southern Coastal Bend regions.
Stems: Ribbed with pubescence.
Leaves: Simple, alternate, deeply dissected and lobed. Pubescent on both surfaces. Petioles also pubescent.
Inflorescence: Numerous heads with white corollas in both ray and disk florets.
Seed: An achene with two small petal-like scales.