Floral Organogenesis in Some Species ofTradescantiaandCallisia(Commelinaceae)

Abstract

The flowers of Tradescantia virginiana, Tradescantia ohioensis, and Callisia navicularis are polysymmetric and comprised of three sepals, three petals, six stamens in two whorls of three, and three connate carpels. Tradescantia and Callisia, as represented in this study, could be distinguished by the relative sizes and shapes of their floral apices. The apex of C. navicularis, for the duration of organ initiation, was considerably smaller and more convex than in either species of Tradescantia. In all three species, the sepals arise, in succession, first. The petals arise next in rapid succession in both Tradescantia species and in very rapid succession or more or less simultaneously in C. navicularis. The carpels arise last in very rapid succession and their connation is evident soon after their initiation. The inner (antepetalous) stamens appear simultaneously with the petals in C. navicularis, and, as with the petals, it is not always clear that these stamens arise sequentially rather than simultaneously. In both Tradescantia species, the inner (antepetalous) stamens arise in rapid succession concurrent with or immediately following the petals. In all three species, emergence of the outer (antesepalous) whorl occurs in rapid succession and usually begins before that of the inner whorl is complete; the last of the outer stamens does not appear until after all inner stamens are present. Therefore, as observed in this study, the two whorls of stamens arise in an overall, although slight, centrifugal sequence. Elsewhere in the family, only centripetal, slightly centripetal, and simultaneous patterns of stamen initiation have been reported. Elsewhere in the monocotyledons, centrifugal androecia are limited to certain polyandrous palm and alismatid genera, all of which are fundamentally different from and are not homologous to the tradescantioid centrifugal androecium.