XVI International Botanical Congess

The Lake Athabasca sand dunes, located in the midst of the boreal forest in northern Canada, have an open sand environment that is characterized by high light intensity and low water availability. Forty boreal taxa exist on these open sands, including ten endemics. Four endemics are willows (Salix brachycarpa Nutt. var. psammophila Raup, S. planifolia Pursh ssp. tyrrellii (Raup) Argus, S. silicicola Raup, and S. turnorii Raup). Although the endemics morphologies indicate a close taxonomic relationship to their associated progenitors, epidermal features are markedly different. Endemic willows have thicker cuticles and prominent epicuticular waxes on abaxial leaf surfaces, but only two have high degrees of pubescence on leaves and young stems. Moreover, the amphistomatous condition is not prevalent among the endemic willows.