Volume 13 > Part 2 > Year 2016 > Page 367 > Compositae (Asteraceae) > Parthenium

Parthenium hysterophorus L.wfo-0000065156

Sp. Pl. 2: 988. 1753; Gagnep., Fl. Indo-Chine 3: 589. 1924; Chang & Tseng, Fl. Reipubl. Popularis Sin. 75: 334. 1979; Grierson & D.G.Long, Fl. Bhutan 2(3): 1622. 2001; Y.S.Chen & D.J.N.Hind, Fl. China 20–21: 877. 2011.

Accepted Name : This is currently accepted.

Description : Annual herb, to 80 cm tall; stems erect, from tap-roots; stiffly appressed white puberulous, branched above, branches ending in inflorescences. Leaves alternate, basal and cauline; basal leaves petiolate, blade ovate to lanceolate, to 17 by 10 cm, 1–2-pinnatifid, lateral segments irregularly and coarsely rounded-dentate or rounded–lobulate, both surfaces white pubescent, glandular dotted; petioles to 7 cm long. Inflorescences open corymbose; peduncles slender, to 2 cm long. Capitula ca 3 mm diam. at flowering; involucres hemispherical, ca 2 by 2 mm; phyllaries 10, biseriate, outer phyllaries 5, green above, inner 5, ovate, ca 2 mm long, ciliate above, scarious; paleae broadly obovate, enclosing florets, apex papillose. Ray florets limbs ca 0.7 by 1.2 mm, 1 modified palea enclosing a modified disc floret attached to either ovary margin. Disc florets many per capitulum; corolla lobes broadly triangular. Achenes 2.2 by 1.1 mm, glandular dotted; pappus ca 0.4 mm long.

Thailand : NORTHERN: Chiang Mai.

Distribution : Native of tropical America (Jamaica – type), introduced into Vietnam, north to Japan (Ryukyu).

Ecology : Weeds of roadsides, waste places and some perennial crops, 200–1,700 m alt. Flowering: April–October, probably all year round.