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Systematics of the Echinocactus polycephalus complex (Cactaceae)


Systematic Botany 22(2): 303-313
Systematics of the Echinocactus polycephalus complex (Cactaceae)
Three morphologically similar North American barrel cacti comprise the Echinocactus polycephalus complex, here defined as including E. parryi, E. polycephalus var. polycephalus, and E. polycephalus var. xeranthemoides. The relationship of E. parryi to E. polycephalus has been suggested without critical examination. The varieties of E. polycephalus 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. polycephalus 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. polycephalus are summarized. Echinocactus parryi and E. polycephalus are herein lectotypified.

Accession: 003292147

DOI: 10.2307/2419459

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