Opuntia cespitosa Rafinesque. Common Eastern Prickly-pear. Phen: May-Jun; Aug-Dec (-Feb). Hab: Limestone and chalk outcrops, dolomite outcrops, glades, sandy or blackland prairies, upland hardwood or mixed hardwood-pine forests in dry, clay soils. Dist: This is the most common species (a tetraploid, 2n = 44) in the eastern United States; it has traditionally been considered conspecific with O. humifusa.

Origin/Endemic status: Native

Other Comments: O. cespitosa is most common west of the Appalachian Mountains and is found throughout most of the Midwestern states, east of the MS river. O. cespitosa can be differentiated from O. humifusa by its yellow tepals that are basally tinged red, crimson or red-brown, as well as dark brown or red glochids and the presence of spines (note: populations in Bibb Co., AL tend to have lighter colored glochids as in O. humifusa or O. mesacantha). Vegetatively, it is most similar to O. mesacantha ssp. mesacantha, from which this allopolyploid may be partially derived, although floral features are quite different, and O. cespitosa does not have the strongly retrorsely-barbed spines common in O. mesacantha. This species also can be confused with certain forms of O. macrorhiza, another putative parent of O. cespitosa; both species have yellow inner tepals basally tinged red adaxially.

Synonymy: = K4, NY, Majure et al (2017); = Opuntia rafinesquei Engelm.; < Opuntia compressa (Salisb.) J.F.Macbr. – RAB; > Opuntia compressa (Salisb.) J.F.Macbr. – WV; < Opuntia compressa (Salisb.) J.F.Macbr. var. compressa – G; > Opuntia compressa (Salisb.) J.F.Macbr. var. fusco-atra (Engelm.) Weniger – Weniger (1984); > Opuntia compressa (Salisb.) J.F.Macbr. var. grandiflora (Engelm.) Weniger – Weniger (1984); > Opuntia compressa (Salisb.) J.F.Macbr. var. microsperma (Engelm.) L.D.Benson; < Opuntia humifusa (Raf.) Raf. – C, F, GrPl, Il, K3, Mi, Pa, Tn, W, WH3; > Opuntia humifusa (Raf.) Raf. – S13, Ward (2009e); > Opuntia humifusa (Raf.) Raf. ssp. minor (Engelm.) R.Crook & Mottram; < Opuntia humifusa (Raf.) Raf. var. humifusa – FNA4, K1, Va, Benson (1982), Doyle (1990); > Opuntia humifusa (Raf.) Raf. var. microsperma (Engelm.) A.Heller; > Opuntia humifusa (Raf.) Raf. var. parva (Coult.) A.Heller; > Opuntia mesacantha Raf. var. microsperma (Engelm.) J.M.Coult.; > Opuntia mesacantha Raf. var. parva J.M.Coult.; > Opuntia opuntia (L.) H.Karst. – S, Britton & Rose (1937); > Opuntia rafinesqueii Engelm. var. microsperma Engelm.; > Opuntia rafinesqueii Engelm. var. minor Engelm.

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Heliophily: 9