1. Erucastrum gallicum (Willd.) O.E. Schulz (dog mustard, rocketweed)
Sisymbrium gallicum Willd.
Pl. 319 d, e;
Map 1350
Plants annual or biennial, terrestrial. Stems 20–75 cm long, erect, branched
from the base, pubescent with unbranched hairs. Leaves alternate and basal, 3–15(–25)
cm long, the upper leaves progressively reduced, petiolate, not clasping, the
leaf blades oblong to oblanceolate, 1 or 2 times pinnately divided, the
divisions usually irregularly toothed, pubescent with unbranched hairs.
Inflorescences panicles, the branches and most of the flowers subtended by
reduced, leaflike bracts. Sepals 2–4(–5) mm long, ascending, narrowly oblong.
Petals 4–7 mm long, not lobed, pale yellow. Styles 1.5–3.0 mm long. Fruits
ascending, straight, 2–4 cm long, more than 10 times as long as wide, linear,
somewhat 4-angled in cross-section, not beaked except for the persistent style,
each valve with a raised, sometimes winglike midnerve, dehiscing
longitudinally. Seeds in 1 row in each locule, 1.2–1.3 mm long, oblong in
outline, not winged, the surface with a fine, netlike or honeycomb-like pattern
of ridges and pits, reddish orange. 2n=30. May–September.
Introduced, Jackson County and the city of St. Louis
(native of Europe, Asia, widely introduced in North
America). Ditches and railroads.
Plants of Erucastrum bear a strong resemblance to some Brassica
species but differ in several subtle morphological features of the
inflorescences, flowers, and fruits (Al-Shehbaz, 1985; Rollins, 1993), in
addition to those presented in the key to genera above.
The spread of E. gallicum in North America
was documented by Luken et al. (1993). The species was first documented in the United States from collections made along
railroads in Wisconsin in 1903, and it was
first collected in Missouri
in 1918. It is presently known from at least 29 states and all of the Canadian
provinces and territories. However, because of heavy herbicide use along
railroads during the past few decades, it probably no longer occurs at many of
its former sites.