Opuntia humifusa (Rafinesque) Rafinesque. Spineless Eastern Prickly Pear. Phen: May-Jun; Aug-Dec. Hab: Slate outcrops, sandy soils, upland hardwood forests or mixed pine-hardwood forests in dry, clay or silty soils. Dist: O. humifusa is restricted primarily to the Appalachian Mountains and mid-Atlantic Coastal Plain, but also occurs in the inner Coastal Plain of c. and nc. MS (Attala, Choctaw, Grenada, Webster cos.).

Origin/Endemic status: Endemic

Taxonomy Comments: More work may illuminate populations in n. AL, nw. GA, w. SC, w. NC, and ne. TN, however, at present populations are disjunct between the eastern states (DE, MD, NJ, VA, WV) and MS. O. humifusa is an allotetraploid (2n=44), cryptic species that is most easily confused with O. mesacantha ssp. mesacantha, from which it can be separated by its lack of spines (although see O. mesacantha), and generally increased number of areoles per diagonal row across the cladode face at midstem (4-5 vs. 3-4 in O. mesacantha), generally inserted glochids (vs. exserted in O. mesacantha), and smaller seeds (4.0-4.6 mm long vs. 5.0-5.9 mm long in O. mesacantha ssp. mesacantha) with a smooth funicular envelop (instead of the upraised funicular envelope in O. mesacantha ssp. mesacantha). Opuntia humifusa also tends to have rotund or elliptic-oblong cladodes vs. O. mesacantha ssp. mesacantha, which more often has rotund to obovate cladodes, but cladode shape is highly variable. Populations of O. humifusa are typically located geographically between populations of O. cespitosa and O. mesacantha ssp. mesacantha. See Kalmbacher (1976) and Leuenberger (1993) for a discussion of the proper name for this taxon.

Synonymy: = K4, NY, Majure et al (2017); > Opuntia calcicola Wherry – WV; < 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. humifusa (Raf.) Weniger – Weniger (1984); < Opuntia humifusa (Raf.) Raf. – C, F, K2, Pa, W, WH3; > Opuntia humifusa (Raf.) Raf. – Ward (2009e); >< Opuntia humifusa (Raf.) Raf. – Tat; < Opuntia humifusa (Raf.) Raf. var. humifusa – FNA4, K1, Va, Benson (1982), Doyle (1990); > Opuntia macrarthra – S; > Opuntia opuntia (L.) H.Karst. – S, S13, Tat

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Heliophily: 9