Rafinesque, Bulletin Botanique 1: 216, 1830
(Also Opuntia mesacantha Raf ssp mesacantha Majure)
What is Opuntia mesacantha?
Opuntia mesacantha is a southeastern prickly pear found in Georgia, Alabama, and Florida and adjacent areas in the southern Piedmant and Gulf Coast Barrier Islands. It is absent in the Florida peninsula. It resembles O. humifusa and O. cespitosa but has distinct differences; see Majure, 2014 and Majure et al, 2012.
O. mesacantha is a prostrate plant that may branch in all directions to 1 m across. Cladodes may be spined or unspined and are smooth in outline, obovate or rotund, occasionally elliptical. Spines are stout (0.95-1.3 mm in diameter).
Flowers are pure yellow with no red. Fruits are reddish at maturity. Seeds are 5.0-5.9 mm long.
O. mesacantha and O. lata are difficult to differentiate in the field, but Adanick et al., 2019 developed a method to measure stomates in the field and differentiate the two taxa easily. See the original description. O. mesacantha is tetraploid, whereas the related O. lata is a diploid. Like other eastern prickly pears, O. mesacantha colonizes sandy or rocky areas that become dry between rains.
Concerning the differences between O. mesacantha and O. humifusa, The Flora of the Southern and Mid-Atlantic States (2015) reports:
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…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. exerted in O. mesacantha), and smaller seeds (4.0-4.6 mm long in O. humifusa vs. 5.0-5.9 mm long in O. mesacantha) with a smooth funicular envelop (instead of the upraised funicular envelope in O. mesacantha ssp. mesacantha).