Santa maria

Parthenium hysterophorus is an erect, much-branched annual or short-lived perennial herb of the Asteraceae family growing 0.3-1.5 m tall with a stout taproot. Stems are striate, longitudinally grooved, sparsely to densely covered with short stiff hairs and become woody at the base in older plants. Leaves are alternate, deeply bipinnatisect to pinnatisect with finely divided, linear-lanceolate ultimate segments giving a feathery overall appearance, 5-20 cm long, pale yellowish-green and softly pubescent on both surfaces. Inflorescences are numerous small, flat-topped corymbose heads borne in much-branched panicles in the upper part of the plant. Individual heads are 4-6 mm across with a hemispherical involucre of two rows of green bracts. Each head bears five small, fertile, three-toothed white ray florets and 12-60 small white tubular but functionally male disc florets. The fruit is a small black, obovate, slightly winged achene bearing two persistent pappus scales and one of the ray petals attached at the apex, dispersing very readily. Native to subtropical North America (south-central US, Mexico, Caribbean) and now an aggressive invasive throughout the tropics and subtropics worldwide.