The Athabasca sand dunes, located on the south shore of Lake Athabasca in northern Alberta and Saskatchewan, Canada, are the largest northern dunes. They were formed (after deglaciation) about 10,000 years ago and were vegetated soon thereafter. Over 200 plant taxa occupy this region, but only 40 occur on open sands. Ten plant species are dune endemics, including four representatives of the genus Salix (Salicaceae). These endemic willows (Salix brachycarpa Nutt. var. psammophila Raup, S. planifolia Pursh ssp. tyrrellii (Raup) Argus, S. silicicola Raup, and S. turnorii Raup) share several morphological features with their putative widespread progenitors. However, certain leaf characters (e.g. amphistomatic leaves, thick cuticles, and high pubescence) of these endemic willows have been described as being 'adaptive' to the open sand habitat. Leaf anatomy and morphology were evaluated for endemic Salix taxa and their progenitors using light and scanning electron microscopy. Salix planifolia ssp. tyrrellii and S. turnorii have amphistomatous leaves, while S. brachycarpa var. psammophila and S. silicicola have the greatest trichome densities. Endemic willows have thicker cuticles than their widespread progenitors. Compact leaf mesophyll in endemic Salix species suggests adaptation to this high light intensity environment.

Key words: Lake Athabasca sand dunes, leaf structure, Salix