Annuals, (1-)10-25(-80) cm (taprooted; often aromatic). Stems 1-10+, usually erect or ascending, sometimes decumbent, branched or not, glabrous or glabrate to sparsely hairy (hairs basifixed). Leaves (not marcescent) basal (soon withering) and cauline; alternate; subpetiolate or sessile; blades spatulate to oblong or ovate (bases sheathing or clasping, often pinnately auriculate), (1-)2-3-pinnately lobed (lobes linear, often curved distally), ultimate margins entire (± recurved), mucronate, faces glabrous or glabrate to sparsely hairy (hairs basifixed). Heads radiate or discoid, borne singly or in open, corymbiform arrays. Involucres patelliform, 4-14 mm diam. Phyllaries persistent, 25-50 in [2-]3-4[-5] series, distinct, oblong or ovate to spatulate or linear-spatulate (membranous, not carinate, bases not indurate), subequal, margins and apices (hyaline) scarious (apices rounded to obtuse). Receptacles conic to oblong-ovoid [subulate] (hollow), epaleate. Ray florets 0 or 10-22, pistillate, fertile; corollas white, laminae elliptic-ovate. Disc florets 120-750+, bisexual, fertile; corollas (persisting in fruit, often slightly asymmetric, sometimes with scattered, sessile, golden glands) yellow to greenish yellow or yellowish green, tubes ± dilated), throats urceolate to campanulate, lobes 4-5 (spreading), deltate [with resin sacs]. Cypselae obconic, slightly compressed (usually asymmetric, apices oblique), ribs [3-]5, faces glabrous, smooth between ribs (pericarps sometimes with myxogenic cells abaxially and/or in ribs; embryo sac development monosporic); pappi 0, coroniform, or (sometimes on ray cypselae) adaxial auricles. x = 9. Matricaria has been confused with Tripleurospermum (see discussion under the latter). Typification of Matricaria was discussed by K. Bremer and C. J. Humphries (1993), who rejected the arguments of S. Rauschert (1974) in favor of the use of Chamomilla over Matricaria.
Heads radiate or discoid, the rays white, pistillate and usually fertile; invol bracts dry, 2-3-seriate, not much imbricate, with ±scarious or hyaline margins; receptacle naked, hemispheric to more often conic or elongate; disk-cors yellow, 4-5-toothed; style-branches flattened, truncate, penicillate; achenes glabrous or roughened, generally nerved on the margins and ventrally, nerveless dorsally; pappus a short crown or none; herbs with alternate, pinnatifid or pinnately dissected lvs and small or middle-sized heads terminating the branches or in a corymbiform infl. 40, N. Hemisphere and S. Afr.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.