Erect annual. Stems ± glabrous, hollow, striate, 15-70 cm high, sometimes tinged purple toward base. Basal lvs moderately to densely hairy below and on petiole, glabrous above, 2-3-pinnate; ultimate segments ovate, pinnatisect, 5-20 mm long, sessile or shortly petiolate; stem lvs similar to basal but reduced, 1-3-pinnate and shortly petiolate. Umbels 2-5 cm diam.; rays 2-5, c. 1-2 cm long; bracts 0-1, linear to triangular; bracteoles 3-5, ovate-acuminate. Fls 2-6, white, 1-2 mm diam. Fr. ovoid, c. 3 mm long, covered with curved spines and tapering to a smooth beak c. 1/4-⅓ length of ovuliferous part; base of fr. at pedicel apex with a ring of hairs.