2. Sinapis arvensis L. (wild mustard, charlock, crunchweed)
Brassica arvensis (L.) Rabenh.
B. kaber (DC.) L.C. Wheeler
B. kaber var. pinnatifida (Stokes) L.C. Wheeler
Pl. 327 a–d; Map
1390
Stems (5–)20–100(–210) cm long. Basal and lower leaves 5–20(–25) cm long,
obovate in outline, usually pinnately divided with 3–11 irregular, toothed
lobes, sometimes only toothed. Upper leaves progressively reduced, the smallest
1–2 cm long, oblanceolate to oblong in outline, usually sessile, the margins
toothed. Sepals (4–)5–6(–8) mm long. Petals (8–)9–12(–17) mm long. Fruits with
the beaks 0.8–1.6 cm long, usually about half as long as the lower portion,
narrowly conical, circular or angled in cross-section, the lower portion of the
fruit (0.6–)1.2–3.5(–4.3) cm long, glabrous or sparsely pubescent with short
hairs fairly uniform in size, usually slightly constricted between the seeds.
Seeds (2–)4–8(–12) per locule, (1.0–)1.4–2.0 mm in diameter, the surface with a
fine, indistinct, netlike or honeycomb-like pattern of ridges and pits, reddish
brown to black. 2n=18. April–July.
Introduced, widely scattered in Missouri (native of Europe, Asia, introduced
nearly worldwide). Edges of crop fields, railroads, roadsides, and open,
disturbed areas.
This species is more common in Missouri than S. alba and is almost
certainly more common in Missouri than present herbarium specimens would
indicate. It is a worldwide weed of crop fields and disturbed ground that is
very difficult to eradicate because of its high production of seeds that are
quite long-lived (Al-Shehbaz, 1985).
Although generally considered an introduced species in North America,
archaeological studies document that S. arvensis was present in the
northeastern United States as early as 8,000 years ago, and it was relatively
abundant and widespread by 2,000 years before the present (Jacobson et al.,
1988). However, it is highly doubtful that seeds of this species can be
determined with certainty from other cultivated mustards especially in
archaeological remains. It is not known whether the plants were grown by Native
Americans at that time or were components of the indigenous flora. Whichever
the case, the species appears to have become extirpated from North America
prior to European colonization, and the earliest collections found in herbaria
are consistent with its status as a weedy introduction, rather than a native
species (Rollins, 1993).