A comparative epidermis study of the Athabasca sand dune willows (Salix; Salicaceae) and their putative progenitors

Abstract

The Athabasca sand dunes are located on the south shore of Lake Athabasca in northern Alberta and Saskatchewan, Canada. Four willow shrubs (Salix; Salicaceae) occur on the open sands, two of which are endemic to the Athabasca sand dunes. Light and scanning electron microscopy were used to quantify stomatal frequency, stomatal index, trichome density, and cuticle thickness, for the Athabasca sand dune willows and their associated putative progenitors. The Athabasca sand dune taxa (Salix brachycarpa var. psammophila, Salix planifolia subsp. tyrrellii, Salix silicicola, and Salix turnorii) occur primarily on the inner dunes, and each has certain leaf epidermal features that appear to be adaptive to the exposed nature of the open sand habitat and the high light intensity. Salix brachycarpa var. psammophila and S. silicicola have tomentose leaves, with trichome densities that are significantly greater than those of their respective widespread progenitors. Salix planifolia subsp. tyrrellii and S. turnorii have amphistomatic leaves and substantially thicker cuticles than their associated progenitors. This investigation is the first to compare adaptive leaf epidermis features within the derivative–progenitor Salix pairs. Considerations for the significance of amphistomaty in the Athabasca sand dune Salix taxa are discussed.Key words: Athabasca sand dunes, cuticle, Salix, stomata, trichomes, willow.