Opuntia humifusa

Opuntia humifusa
Opuntia humifusa

(Rafinesque) Rafinesque, Flora Medica (or Manual of the Medical Botany of the United States of North America) 2: 247, 1830

Lectotype; HerbariumHerbarium; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; HerbariumDrawing (Curtis’s Botanical Magazine, vol. 50: pl 2393, 1823 [as Cactus opuntia]); Drawing (Audubon, Birds of America [double elephant folio edition, plate 94, as Cactus opuntia] ca. 1830) 

See O. cespitosa  See O. lata  See O. mesacantha

Details

Opuntia humifusa has been lumped with a variety of southeastern prickly pear species including O. cespitosa, O. mesacantha, and O. lata, but it is a distinct species. The cactus ranges from New England to Virginia (Georgia?). O. humifusa is essentially spineless.  Flowers are yellow. Britton and Rose referred to the species as O. opuntia and mention that it is native to multiple eastern states. Read the original citation. Opuntia humifusa is tetraploid, but diploid populations are reported (see below, Cytogeography). Variation in ploidy suggests that there may be different taxa lumped under the name O. humifusa

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O. humifusa is not a desert plant. Rather, it is often an opportunist in areas that receive heavy rainfall or runoff part of the year but which are hot and dry other parts of the year. Hence, it is often found growing on rocky outcrops. 

Over the past few centuries, O. humifusa may have been referred to by well over a dozen synonyms including: Cactus humifusus, O. pollardii, O. allairei, O. calcicola, O. cespitosa, O. compressa, O. fusco-atra, O. italica, O. mesacantha, O. nemoralis, O. rafinesquii var. minor, O. rafinesquii, O. rubiflora, O. vulgaris var. rafinesquii, and O. vulgaris. Some of these are independent species in their own right including: O. cespitosa, O. lata, and O.  mesacantha.

New Evidence

Several scientific publications by Dr. Majure (Cytogeography, Mississippi, Ecology, Taxonomic Revision, and Evolution) provide new information about O. humifusa and related plants. A new understanding is emerging. O. humifusa s.l. is a constellation of similar-appearing taxa–a collection of species that originated through hybridization.

See also O. cespitosa, O. mesacantha, and O. lata. These eastern plants are all similar to O. humifusa and were once, and perhaps still are, confused with it. 

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