Trifolium pratense L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Short-lived perennial, ascending or suberect, to 8 dm, the stem appressed-hairy; stipules oblong, the free part short, abruptly narrowed to a short awn; lower lvs long- petioled, upper short-petioled to sessile; heads sessile or on peduncles to 2 cm, globose to round-ovoid; fls 13–20 mm; cal glabrous to sparsely pilose, the tube 3–4 mm, the lobes setaceous, one 4–7 mm, four 2–5 mm; cor magenta, varying to nearly white; standard obovate-oblong, equaling or a little longer than the oblong obtuse wings; 2n=14. Native of Europe, widely cult. and escaped in fields and roadsides nearly throughout temperate N. Amer. May–Aug.