Engelmann & Bigelow, Proceedings of the American Academy of Arts and Sciences 3: 298, 1856
Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Holotype (O. basilaris brachyclada); Herbarium (O. basilaris brachyclada); Herbarium (O. basilaris brachyclada); Herbarium (O. basilaris brachyclada); Herbarium (O. basilaris longiareolata); Herbarium (O. basilaris longiareolata) Herbarium (O. basilaris longiareolata); Herbarium (O. basilaris longiareolata); Isolectotype (O. basilaris ramosa); Herbarium (O. basilaris heilii)
O. basilaris is a distinctive plant; it has the archetypical “beaver tail” cactus look. The cladodes form dense clumps 5- to 20-inches tall and 1(5)-ft across. The pads are blue-green and roudish or wedge shaped and 5- to 8(10)-inches long. Often the cladodes are fan shaped, but they may be oval, obovate or even elongate-obovate. The pads of the major variety (basilaris) arise from a single point and are arranged in an irregular rosette. The areoles are slightly sunken. There are at least 5 described varieties:
All varieties are spineless except var treleasei. O. basilaris basilaris is by far the most commonly enocuntered variety. Read the original description of O. basilaris. O. basilaris is diploid, but O. basilaris treleasii is triploid and may represent a separate taxon.
The blue-green or gray-green pads are distinctive and may have hints of purple, or they may be entirely purple under stress. Though spineless, there are numerous glochids that, once embedded, are seemingly impossible to remove from skin. Native Americans used O. basilaris as a medicinal plant (Anderson, 2001). The plant has bright magenta flowers and is a favorite in western gardens because of its unique shape, pad colors, and flowers.
Britton and Rose discuss several varieties that are not recognized here including: albiflora, coerulea, and nanna.