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Systematics of the Echinocactus polycephalus Complex (Cactaceae)

1997; American Society of Plant Taxonomists; Volume: 22; Issue: 2 Linguagem: Inglês

10.2307/2419459

1548-2324

Michael Chamberland,

Botany, Ecology, and Taxonomy Studies

Three morphologically similar North American barrel cacti comprise the Echinocact is polycepha- lus complex, here defined as including E. parryi, E. polycephalus var. polycephaluts, and E. polycephalits var. xeranthemoides. The relationship of E. parryi to E. polycephaluts has been suggested without critical examination. The varieties of E. polycephaluis have been elevated to species rank by some taxonomists; however existing keys have shown inadequacies separating these taxa in the field, and distribution maps have indicated potential sympatry among them. Herbarium studies, field observations, scanning electron microscopy, and phenetic analysis are here used to support the distinction of E. parryi and E. polycephaltis as separate species. The varietal ranking of E. polycephalus var. xeranthemoides is also supported. The varieties of E. polycephalus are distinguished by seed and hypanthium scale morphology. Their distributions are parapatric, with evidence of hybridization and potential introgression. The records of Pleistocene-age seed macrofossils of E. polycephalits are summarized. Echinocactus parryi and E. polycephaluts are herein lectotypified.