Annuals (biennials) [perennials, subshrubs], mostly 5-90 cm (often aromatic). Stems 1-5+, erect to decumbent, usually branched, strigillose or strigoso-sericeous to villous (hairs medifixed), glabrescent [glabrous or sericeous to lanate]. Leaves mostly cauline; alternate; petiolate or sessile; blades ± obovate to spatulate, 1-3-pinnately lobed, ultimate margins dentate to lobed, faces glabrous or strigillose to villous [glabrous or sericeous to lanate]. Heads radiate [discoid], borne singly or in lax, corymbiform arrays (peduncles sometimes clavate and/or curved in fruit). Involucres obconic to hemispheric or broader, 5-13[-20] mm diam. Phyllaries persistent, mostly 21-35+ in 3-5 series, distinct, deltate to lanceolate, oblong, or elliptic, unequal, margins and apices (hyaline and colorless or brownish [black]) scarious. Receptacles hemispheric to narrowly conic, paleate (wholly or only distally); paleae ± flat, scarious to indurate (subulate or elliptic to obovate with mucronate to acuminate-spinose tips). Ray florets [0 or 2-]5-20[-30+], pistillate and fertile or styliferous and sterile; corollas usually white, rarely yellow or pink, laminae mostly oblong (tubes sometimes hairy). Disc florets (60-)100-300+, bisexual, fertile; corollas usually yellow, rarely pink, tubes ± cylindric (usually proximally dilated, ± spongy in fruit, sometimes hairy, not saccate), throats funnelform, lobes 5, ± triangular (abaxially minutely crested). Cypselae obovoid to obconic or turbinate (circular or 4-angled in cross section), ribs usually 9-10 (0) and smooth or tuberculate, faces glabrous (pericarps with myxogenic cells); pappi 0 or coroniform. x = 9. Anthemis secundiramea Bivona-Bernardi, a European species, was collected once in Virginia; it differs from A. arvensis in having peduncles to 8 cm and ribs on cypselae ± tuberculate.
Heads radiate or rarely discoid, the rays elongate, white or yellow, pistillate or neutral; invol bracts subequal or more often imbricate in several series, dry, the margins ±scarious or hyaline; receptacle convex or conic or hemispheric, chaffy at least toward the middle; disk-fls numerous, perfect, the tube usually cylindric at base, occasionally flattened; style-branches flattened, truncate, penicillate; achenes terete or 4-5- angled, or occasionally ±compressed but not callous-margined; pappus a short crown, or more often none; herbs, usually aromatic, with alternate, incised-dentate to pinnately dissected lvs and medium-sized to rather large heads terminating the branches. 60, Old World.
Besides the spp. treated below, A. mixta L. (annual; rays pistillate, white with yellow base) and A. nobilis L. (perennial; rays pistillate, white, receptacular bracts blunt) have been found as waifs in our range.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.