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.