Monographs Details: Opuntia macrorhiza Engelm.
Authority: Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Description:Species Description - Prostrate and spreading, forming mats to 1.5 m wide; usually some roots tuberous-thickened; joints of the stem mostly 6–10 × 5–7 cm, flat, orbicular to obovate; areoles on full-grown joints 15–30 mm apart, with (1–)3–6 spines 3.5–5.5 cm; fls yellow with reddish center, 5–7 cm wide; outer sep ovate, acute to acuminate; fr reddish-purple, 2.5–4 cm, juicy; seeds discoid with a rough, irregular, corky margin. Prairies and plains; S.D. to Ariz. and Tex., e. occasionally to Wis., s. Mich., Ill., and reputedly O. and Ky. May–July. (O. mesacantha; O. tortispina, misapplied)
O. polyacantha Haw., a similar western sp. with 6–10 spines per areole and dry frs, has been reported e. to Wis. and Mo.
Common Names:Plains prickly pear