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(American Journal of Botany. 2001;88:68-75.)
© 2001 Botanical Society of America, Inc.

Stamen dimorphism in Rhododendron ferrugineum (Ericaceae): development and function1

Nathalie Escaravage2, Elisabeth Flubacker2, André Pornon3, Bernard Doche2 and Irène Till-Bottraud2

2 Laboratoire de Biologie des Populations d'Altitude CNRS-UMR 5553, Université Joseph Fourier, B.P. 53, F-38041 Grenoble Cedex 09, France; and 3 Laboratoire d'Ecologie Terrestre CNRS-UMR 5552, Université Paul Sabatier, Zoologie Ecologie, Bât. 4R3, 118, route de Narbonne, F-31062 Toulouse Cedex 04, France

The function of stamen dimorphism in the breeding system of the alpine shrub Rhododendron ferrugineum was studied in two populations in the French Alps. This species has pentameric flowers with two whorls of stamens: an inner whorl of five long stamens and an outer whorl of short stamens. We studied the development of stamens from buds to mature flowers (measurement of the filament, anther, and style lengths at five successive phenological stages) and compared the size and position of reproductive organs at maturity in control and partially emasculated flowers (removal of long-level stamens) to determine whether the presence of long-level stamens constitutes a constraint for the development of the short-level ones. Stamen dimorphism can be observed early in stamen development, from the bud stage of the year prior to flowering. At this early stage, meiosis had already occurred. Emasculation of the long-level stamens induced the short-level ones to grow longer than in normal conditions. We also performed seven pollination treatments on ten randomly chosen individuals in each population, and the number of seeds following each treatment was recorded. Results from these treatments showed that R. ferrugineum produced spontaneous selfed seeds in the absence of pollinators. However, no seed was produced when short-level stamens were emasculated and pollinators excluded, suggesting that long-level stamens are not responsible for selfing in the absence of pollinators and that reproductive assurance is promoted by short-level stamens.

Key Words: Ericaceae • pollination system • reproductive assurance • Rhododendron ferrugineum • stamen development • stamen size




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