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DOI

10.5642/aliso.20001902.04

First Page

165

Last Page

179

Abstract

Yuccas (Yucca, Agavaceae) are an easily recognizable constituent of the vegetation of the International Four Corners; an area made up of portions of Arizona, New Mexico, Sonora and Chihuahua. We recognize three species as native to the region, Yucca baccata, Y. elata and Y. madrensis, together with interspecific hybrids, and document for the first time naturally occurring intersectional hybridization between baccate-fruited (sect. Yucca) and capsular-fruited (sect. Chaenocarpa) species. We examine the reproductive barriers to hybridization operating within the genus, i.e., spatial, temporal and ethological, and we consider circumstances that may have been responsible for the production and widespread distribution of hybrids in the IFC. These include establishment of sympatry, pollinator biology, founding hybrids and human activities. We also reflect on the present situation regarding sexual reproduction in species of Yucca in the Southwest.

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© 2000 Lee W. Lenz, Michael A. Hanson

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