Subdioecy in Consolea spinosissima (Cactaceae): breeding system and embryological studies

Abstract

The breeding system and the embryology of Consolea spinosissima, a tree-like opuntioid endemic to Jamaica, were investigated. Morphological and embryological studies revealed that the species is subdioecious, with three sexual morphs present in the 150 × 120 m plot studied at Hellshire Hills, Jamaica. The female morph has pistillate flowers with open stigma lobes, no pollen grains, and sets fruit. The male morph has cryptic staminate flowers with closed stigma lobes, viable pollen grains, and a nonfunctional gynoecium that does not set seed. The weak hermaphrodite morph has low fruit set and "perfect" flowers that superficially resemble the functionally staminate flowers of the male morph. These perfect flowers reach anthesis with viable pollen grains, with no or only a few functional ovules, and with the style supporting pollen tube growth. Embryological studies showed that the critical stage for sex determination occurs earlier in pistillate than in staminate and perfect flowers. Anthers of pistillate flowers abort prior to microspore tetrad formation, whereas ovules of the staminate and perfect flowers degenerate after the complete maturation of the embryo sac. Based on flower structure and embryological data, we hypothesize that the ancestor of C. spinosissima is/was hermaphroditic.