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Leaf thicknesses of Salix taxa (Salix brachycarpa Nutt. var. psammophila Raup, Salix planifolia Pursh subsp. tyrrellii (Raup) Argus, Salix silicicola Raup, and Salix turnorii Raup) from the Athabasca sand dunes in northern Saskatchewan, Canada, were evaluated and compared with those of their respective widespread progenitors (S. brachycarpa Nutt. var. brachycarpa, S. planifolia Pursh subsp. planifolia, Salix alaxensis (Anders.), and Salix eriocephala Michx. var. famelica (C. R. Ball) Dorn). Leaf thickness was measured using standard light microscopy, and results were compared with the occurrence of amphistomaty in these Salix species. Leaf thickness values varied among the species and differed significantly within each derivative–progenitor Salix pair. The two amphistomatic taxa from Yakow Lake dunes, S. turnorii and S. planifolia subsp. tyrrellii, had significantly thicker leaves (337.65 ± 5.99 µm and 226.00 ± 5.22 µm, respectively) than their widespread progenitors, as well as the thickest leaves overall. The data comparison indicates a relationship between amphistomaty and leaf thickness among the Salix taxa, as thicker leaves tend to be amphistomatic. [ABSTRACT FROM AUTHOR]