Counting nodes: timing of flowering in the annual Rhinanthus angustifolius

The genus Rhinanthus is known for its extensive variation in flowering time. Within many of the species, several ecotypic variants are distinguished. Vernal ecotypes flower early, have few branches and are relatively small. Aestival plants are bigger, have more branches and flower in mid-season, while autumnals have many branches and flower late. It has been recognised that these differences, which persist in common gardens, are linked to the number of nodes produced before the first flower, vernal plants producing few nodes and autumnals many. My research is aimed at determining what underlies variation in flowering time within a vernal population of Rhinanthus angustifolius. Can within-population differences in flowering time be explained by differences in node number, just as among ecotypes, or does variation in the timing of germination or in growth rate contribute as well? Autumnal ecotypes have a much higher reproductive output than vernal plants. Does flowering time have an effect on plant fitness within a vernal population, are there differences in seed production between early and late flowering plants? What is the heritability of the number of nodes under the first flower? These questions will be answered by observations on flowering time and fitness in a natural population, and experiments in greenhouse and garden.