Annuals; densely hispid at least proximally. Stems erect, branched distally, (2-)3.5-12 (-17.5) dm, often densely hispid proximally, (trichomes retrorse), usually glabrous distally. Basal leaves rosulate; petiole 1-4(-5) cm; blade broadly oblanceolate (in outline), (1.5-)2.5-8(-12) cm × (10-)20-50(-70) mm, margins runcinate to lyrate-pinnatifid; lobes 2-4 on each side, much smaller than terminal lobe, margins entire or dentate, (terminal lobe triangular, often hastate). Cauline leaves similar to basal; blade (much smaller than basal, to 1.5 cm wide), margins entire or toothed. Fruiting pedicels divaricate or ascending, slender, narrower than fruit, 5-12(-15) mm. Flowers: sepals ascending, oblong, 3-4 × 1-1.5 mm; petals spatulate, 6-8 × 2-3 mm, claw 2.5-3.5 mm; filaments 3-4.5 mm; anthers ovate, 0.6-1 mm. Fruits (ascending to suberect, young fruits not overtopping flowers), narrowly linear, curved or straight, subtorulose, slender, 2-3.5(-5) cm × 0.9-1.1 mm; valves often glabrous; ovules 40-60 per ovary; style stout, 0.3-0.7 mm; stigma prominently 2-lobed. Seeds 0.7-1 × 0.5-0.6 mm. 2n = 14.
Annual herb with a large taproot 0.5 - 1.2 m tall Stem: upright, branched above, hairy below. Flowers: in dense, branched, elongated clusters (racemes), which are borne terminally on the stems. Mature flower stalks divergent, 5 mm - 2 cm long. Sepals four, spreading, free (not touching), yellow, 3 - 4 mm long, linear to linear-oblong, tips with a small protrusion (protrusion has a single hair). Petals four, free (not touching), yellow, 5 - 8 mm wide, bases narrowed. Stamens six, upright. Anthers yellow. Fruit: a long, narrow pod (silique), stalks thin, ascending to upright, 1 - 5 cm long, cylindrical, with a beak. Seeds in one row in each chamber. Lower leaves: alternate, pinnately divided (lyre-shaped), stalked, to 15 cm long, to 6 cm wide, toothed, usually hairy. Lateral segments spreading or bent abruptly downward (deflexed), triangular to egg-shaped, tips pointed. The terminal segments are larger and triangular. Upper leaves: alternate, less pinnately divided or lobed than lower leaves, stalked, smaller than lower leaves, reduced upward, tips pointed, usually hairy.
Similar species: No information at this time.
Flowering: mid-May to early November
Habitat and ecology: Introduced from Asia. A weed of high-nitrogen habitats, such as barnyards, which is becoming more common in the Chicago Region. Also look for it in waste ground, disturbed areas, and along roads and railroads.
Occurence in the Chicago region: non-native
Etymology: Sisymbrium is the Ancient Greek name for various plants. Loeselii is named after Johannes Loeselius (1607-1657), a German botanist and physician.
Erect, 5-12 dm, the stem generally reflexed-hirsute below; lower lvs lyrate-pinnatifid and dentate, usually hirsute, the lateral segments triangular to ovate, acute, spreading or deflexed, the terminal one larger, triangular; infl elongating progressively, the fls and buds overtopping the frs; sep 3-4 mm; pet lemon-yellow, 5-8 mm; anthers ca 1.5 mm; mature pedicels divergent, 5-20 mm; frs ascending to erect, slender, terete, 1.5-4 cm; 2n=14. Native of se. Europe and w. Asia, occasionally found in our range, and becoming a weed in w. U.S. June-Aug.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.