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Functional Dioecy in Echinocereus coccineus (Cactaceae): Breeding Systems, Sex Ratios, and Geographic Range of Floral Dimorphism

M. Timm Hoffman
American Journal of Botany
Vol. 79, No. 12 (Dec., 1992), pp. 1382-1388
Stable URL: http://www.jstor.org/stable/2445137
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Functional Dioecy in Echinocereus coccineus (Cactaceae): Breeding Systems, Sex Ratios, and Geographic Range of Floral Dimorphism
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Abstract

The breeding system of the hedgehog cactus, Echinocereus coccineus Engelm. (Cactaceae), was studied at two sites in the northern Chihuahuan Desert, New Mexico. Two distinct flower types, restricted to separate plants, were observed. One was hermaphroditic and the other male-sterile. Hand-pollinations and field observations showed them to be functionally male and functionally female, respectively. There were significant quantitative intersexual differences in floral morphology. The main pollinators of the populations studied are probably two species of halictid bee. Sex ratios based on the number of plants and flowers at the two sites did not differ significantly from 1:1. Significant differences in fruit set existed between functional female plants from the two sites. The floral dimorphism described here appears confined to eastern and northwestern populations, at the periphery of the range of E. coccineus. Floral dimorphism was not observed in three closely related species.

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