1. Anthemis arvensis L. (corn chamomile)

Pl. 224 f; Map 939

Plants aromatic with a pleasant, sweet to musky odor. Stems 10–40(–60) cm long, erect, ascending, or spreading with ascending tips, usually branched throughout or mainly below the midpoint. Leaf blades 1–4 cm long, oblanceolate to oblong-elliptic or ovate, deeply 1 or 2 times pinnately lobed, the basal lobes sometimes appearing fascicled, the ultimate segments 0.5–4.0 mm long. Heads mostly long-stalked, the stalks 3–15 cm long at flowering. Involucre 2.5–5.0 mm long. Receptacle with chaffy bracts throughout. Ray florets pistillate, the corolla 5–15 mm long, sometimes inconspicuously glandular. Disc florets with the corolla 1.5–4.0 mm long, the lobes often minutely glandular. Fruits 1.7–2.2 mm long, the ribs smooth or slightly uneven. 2n=18. May–October.

Introduced, uncommon in the eastern half of Missouri and Jackson County (native of Europe, introduced widely in the U.S. and adjacent Canada, except some southwestern states). Margins of ponds and banks of streams; also railroads, roadsides, and open, disturbed areas.

Plants with chaffy bracts noticeably shorter than the disc florets, which include most North American specimens, have been called var. agrestis (Wallr.) DC. Those with the chaff about as long as or longer than the disc florets are var. arvensis. Steyermark (1963) included var. arvensis for Missouri on the basis of a single specimen collected by Viktor Mühlenbach in the St. Louis railyards; that specimen unfortunately could not be relocated during the present study. This character seems relatively variable, although none of the Missouri materials examined to date have the chaffy bracts distinctly longer than the disc florets. Elsewhere, the overall bract length also more or less correlates with an awnlike tip on the longer bracts and merely a narrowly pointed tip on the shorter ones, but none of the Missouri plants examined appear to possess awns.