O. Acanthium: biennial; stem erect, many-headed, 4-5 feet high, woolly, with broad spinous wings, branched; leaves elliptic-oblong, woolly on both sides, sinuate, spiny, decur-rent; involucre nearly globose, large, somewhat cottony, the scales fringed with minute spinous teeth; florets purple. - Cotton Thistle. - Waste ground. Fl. August, September.