COOPER, RANESSA L.* AND DAVID D. CASS. Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9. - Leaf structure of Salix species (Salicaceae) endemic to the Lake Athabasca sand dunes of northern Saskatchewan, Canada.
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