Flower development in Fedia graciliflora and Valerianella locusta (Valerianaceae)

Abstract

Valerianaceae provides a model clade for examining diversification in floral shape, especially involving size, bilateral symmetry, asymmetry, and handedness. Fedia species have pink, strongly bilaterally symmetrical corollas while Valerianella species generally have white, near-radially symmetrical corollas. In this study we examine the early floral ontogeny of Valerianella locusta and Fedia graciliflora to compare early growth and developmental traits that may lead to the difference in their mature flowers. Fedia graciliflora and V. locusta inflorescences at varying stages of development were collected and dissected to remove subtending bracts and bracteoles. Images of floral development were taken using a stereomicroscope and a Scanning Electron Microscope. The inflorescence primordium appears to continuously bifurcate as it grows, resulting in an inflorescence with densely packed flowers of varying ages. Flowers of both F. graciliflora and V. locusta initiate petals and stamens simultaneously on a ring-like common primordium. We demonstrate that stamen primordia arise in a spiral pattern, grow faster than other organs, and dominate growth until they are nearly mature. Five petal primordia and two stamens arise in F. graciliflora. In contrast, in V. locusta which has three stamens, four petal primordia initiate, which appear as an open ring-like or U-shaped primordium with a furrow on one side. This likely provides the space for the additional large stamen. Sepal development is not evident and lobes are lacking. The gynoecium does not begin to develop until the flower bud is nearing maturity. These data provide a framework for future developmental genetic work in these species.