@mastersthesis {43515,
	title = {Structural adaptations of willows (Salix; Salicaceae) endemic to the Athabasca sand dunes},
	volume = {Biological Sciences},
	year = {2001},
	pages = {75},
	address = {University of Alberta},
	abstract = {The Athabasca sand dunes, located on the south shore of Lake Athabasca in northern Alberta and Saskatchewan, formed (after deglaciation) about 10,000 years ago and were vegetated soon thereafter. Only 40 plant species occur on open sands, including ten endemics; four of these endemics are willows ( 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) are morphologically similar to their putative progenitors. However, endemic Salix taxa have certain structural features that are considered to be adaptive to the open sand habitat. Light and scanning electron microscopy were used to study leaf epidermal features and vessel element (VE) characters in the four endemic Salix taxa. These data were compared with those of the respective putative progenitors. Salix planifolia ssp. tyrrellii and S. turnorii have amphistomatic leaves, and S. brachycarpa var. psammophila and S. silicicola have the greatest trichome densities. Endemic willows have thicker cuticles than their widespread progenitors, as well as abaxial epicuticular wax deposits. Salix brachycarpa var. brachycarpa and its derived endemic, var. psammophila , had the highest VE densities of all endemic-progenitor pairs in this study. Vessel element lumen diameter of the endemic S. planifolia ssp. tyrrelli was significantly less than that of its putative progenitor, and S. turnorii had significantly greater values for both VE lumen diameter and length than its associated progenitor. Vessel element clustering did not differ significantly between endemic and progenitor taxa with the exception of S. silicicola and its progenitor. Amphistomatic leaves, dense trichome coverings, and thick, waxy cuticles exhibited by the endemic willows suggest adaptation to high light intensity, while VE observations correlate with the sandy environment. This is the first detailed study addressing structural adaptations of endemic willows to the Athabasca sand dunes. Structural similarities within each endemic-progenitor Salix pair provide additional support for the close, evolutionary relationships. Structural data, combined with the use of molecular techniques, will aid in elucidating the putative taxonomic status of each endemic-progenitor Salix pair.},
	url = {http://search.proquest.com/docview/304739678},
	author = {Cooper, Ranessa Lea}
}
