[An evolutionary interpretation of the Opuntia robusta sexual polimorphism]
1988
Castillo, R.F. del | Gonzalez Espinoza, M.
Opuntia robusta (Cactaceae) is a prickly pear abundant in central Mexico and used for forage or human consumption. This species produces male, female, and hermaphrodite individual, occasionally in the same populations. We describe the main floral traits of each of the three sexual morphs. Unisexual individuals are heterostylic: male flowers have a long style and a hypotrophied stigma, while females are short-styled with a well developed stigma. This dimorphism allows for relatively easy pollen removal from males, and easy pollen deposition on female stigmas. Hermaphrodites have a medium-size style and a well developed stigma. All three morphs produce nectar. We observed a trend towards a larger nectar production by hermaphrodites, atrributable to their larger receptacles. Flowering occurs during spring, and lasts ca. 15, 13 and 8 weeks in males, females and hermaphrodites, respectively. The flowers are visited mainly by bees and beetles; the former can cross-pollinate the flowers, the latter autopollinate them. An evolutionary interpretation of heterostyly, doecy, and the flowering patterns of O. robusta sexual morphs is presented within the context of current sexual selection theory in plants.
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