Brassica rapa L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Annual to 8 dm, green and sparsely setose-hispid, at least along the lf-margins and the midrib beneath; lower lvs petioled, pinnately ± lobed; upper lvs oblong to lanceolate, dentate or entire, sessile and clasping; fls 1 cm wide; mature pedicels widely ascending, 1–2 cm; frs ascending to suberect, terete or nearly so, 3–5 cm, the slender beak 8–15 mm; seeds 1.5–2 mm, minutely roughened; 2n=20.
B. rapa as here defined includes the field-weed (often called B. campestris L.) and a number of cultivars derived from it, notably turnip and bird’s rape. The related sp. B. oleracea L., glabrous and glaucous, 2n=18, includes a host of cultivars (cabbage, cauliflower, broccoli, Brussels sprouts, etc.) derived from a wild European form that is often segregated as B. sylvestris (L.) Mill. Rape and rutabaga are referred to B. napus L. (2n=38), thought to be an alloploid of the other two spp. Infraspecific nomenclature here is tangled.