9. Arabidopsis suecica (Fries) Norrlin, Meddel. Soc. Fauna Fl. Fenn. 2: 12. 1878; Arabis suecica Fries, Summ. Veget. Scand. I, 30, 147. 1846; A. arenosa (Linnaeus) Scopoli subsp. suecica (Fries) Ahlfvengren in Neuman & Ahlfvengren, Sveriges Flora 453. 1901; A. arenosa var. suecica (Fries) Cajander in Mela, Suomenkasvio, ed. 5, 295. 1906; Cardaminopsis suecica (Fries) Hiitonen ex Hylander, Forteckn. Skand. Vaxt., 1. Karlvaxter, 62, 139. 1941; Hylandra suecica (Fries) Á. Löve, Svensk Bot. Tidskr. 55: 215. 1961; Sisymbrium suecicum (Fries) Nyman, Consp. Fl. Europ. 44. 1878; Stenophragma suecicum (Fries) Celakovsky ex Prantl in Engler & Prantl, Pflanzenfam. 3(2): 192. 1891. TYPE: Sweden. Pro v. Södermanland: Strängnäs, Fries s.n. (lectotype, UPS; see Löve, 1961).
Herbs, annual. Stems (5–)10–45(–60) cm, erect, 1–5(–8) from the base, usually branched above, basally pilose with simple trichomes to 1 mm, apically glabrous. Basal leaves rosulate; petiole (0.3–)0.6–2(–2.8) cm, ciliate; leaf blade obovate to oblanceolate, (0.3–)0.7–3(–4) x (0.1–)0.2–1.4(–1.7) cm, sparsely to densely pubescent with simple and short-stalked forked trichomes, rarely subglabrous, margin lyrate to pinnatifid on each side with 3–6 lateral lobes much smaller than terminal one, rarely dentate, apex obtuse to subacute; cauline leaves 3–8, short petiolate or uppermost sessile; blade lanceolate, oblong, or linear, middle ones (0.3–)1–2.5(–4) x 0.1–0.8(–1.3) cm, margin dentate on lower leaves, entire on upper ones, apex acute to obtuse. Fruiting pedicels slender, divaricate, straight, 5–10(–15) mm. Sepals 1.5–2.2(–2.5) mm, glabrous or distally sparsely pilose with simple trichomes, lateral pair saccate; petals white to lavender, spatulate, 4–5(–6) x 1.5–2.5 mm, apex obtuse or truncate; claw short, not toothed; filaments white, 2.5–4 mm; ovules 40–70 per ovary. Fruits linear, subterete to slightly compressed, smooth to slightly torulose, (2–)2.5–3.5(–4.5) cm x 0.5–0.8 mm; valves with a distinct or obscure midvein; style to 0.5 mm; gynophore to 0.5 mm. Seeds oblong, slightly compressed, light to reddish brown, 0.5–0.8 mm; cotyledons obliquely incumbent. 2n = 26.
Habitats: fields, roadsides, slopes, moist forest margins, grassy areas.
Elevation: 0–600 m.
Distribution: Fennoscandinavia and the Baltic region but perhaps native only in Finland, adventive in adjacent NW Russia, Estonia, NE Denmark, Sweden, Norway, and N Germany (see Jalas & Suominen, 1994).
Note: Arabidopsis suecica is an amphidiploid produced since the last glacial maximum from the hybridization of A.thaliana and diploid A. arenosa (Mummenhoff and Hurka, 1994, 1995; O’Kane et al., 1997, and references therein).