Foetid chamomile

Anthemis cotula, the foetid chamomile, stinking chamomile, mayweed, or dog-fennel, is a strongly malodorous annual herb in the family Asteraceae native to Europe and the Mediterranean basin and now widely naturalized as a weed of arable land, farmyards, roadsides, and disturbed ground across temperate North America, Australia, and elsewhere. The plant is superficially similar to the related and benign German chamomile (Matricaria chamomilla) but is distinguished by its disagreeable acrid smell when bruised, which has earned it numerous derogatory common names. Plants are erect or ascending, 20-60 cm tall, with much-branched glabrate to slightly pubescent stems. Leaves are alternate, 2-5 cm long, two- or three-times pinnately dissected into very narrow linear or filiform segments, almost glabrous, with a finely divided fern-like appearance. The flower heads are borne singly on long peduncles at the branch tips, each 2-3 cm across, with 10-16 white ray florets that quickly become reflexed downward as the head matures, and a central conical receptacle of bright yellow disc florets. Diagnostically, the receptacle of A. cotula is convex-conical and bears thin chaffy scales only among the central disc florets (not throughout, as in true Anthemis species), and the foliage produces blistering of the skin on prolonged contact in some people.