Dunbible-weed

Ambrosia psilostachya, the western or perennial ragweed, is an erect aromatic perennial herb of the family Asteraceae spreading aggressively by creeping rhizomes to form extensive colonies. The slender, branched, hairy stems typically reach 0.3-1 m but can exceed 2 m, bearing alternate to sub-opposite, deeply pinnatifid leaves up to 12 cm long with narrow, pointed lobes and a greyish, hairy texture on both surfaces. From early summer into autumn the plant produces slender terminal spikes of small, nodding, greenish-yellow male flower heads, with inconspicuous female flower clusters in the upper leaf axils that develop into single-seeded ovoid burs. Widely distributed across the United States, Canada, and northern Mexico, it has also naturalised in Europe, temperate Asia, and elsewhere, thriving in prairies, roadsides, and disturbed ground.