Potential roles of scaling and post-anthesis developmental changes in the evolution of floral forms of Eucnide (Loasaceae)

Six of the fourteen species of Eucnide (Loasaceae) are investigated to understand the potential roles of size scaling and post-anthesis ontogenetic changes in the evolution of the floral diversity that characterizes the genus. Principal components analysis of quantitative aspects of mature flowers showed that most of the measured floral features strongly covary and that size was responsible for most of the quantitative variation among the investigated species. Size scaling trends were further investigated by using bivariate comparisons. Scaling trends are strongest among species of sect. Eucnide . Stamen and style length, the most strongly scaled features, have a nearly isometric relationship (slope = 1) in the evolution of the genus. Given this strict scaling which would probably promote self-pollination, it appears that cross-pollination in the genus is most likely to be associated with the evolution of large flowers, compounded by protogyny and differential elongation of stamens and style during post-anthesis ontogeny. Common changes during post-anthesis development include failure of the corolla to spread and variations in the relative elongation patterns of the corolla, stamens, and style.