COOPER, RANESSA L.*, SENNAIT A. YOHANNES, and DAVID D. CASS. Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E9. - A structural study of the rare willow, Salix planifolia ssp. tyrrellii, from the Athabasca sand dunes of northern Alberta.
Salix planifolia ssp. tyrrellii, from the Athabasca sand
dunes, has been considered to be a recent derivative of the widespread
S. planifolia ssp. planifolia. It is endemic to the
Athabasca sand dunes of northern Saskatchewan and was documented
recently from the Maybelle River and Richardson dunes in Alberta.
Salix planifolia ssp. tyrrellii and its putative
progenitor are similar in appearance and can be difficult to
distinguish. A diagnostic feature of S. planifolia ssp.
tyrrellii is the presence of adaxial stomata. In specimens of
S. planifolia ssp. tyrrellii from each of the Athabasca
sand dunes in northern Alberta, adaxial and abaxial stomatal
frequencies were examined. In addition, vessel element (VE) characters
were evaluated, including VE density, VE lumen diameter, VE length,
and VE clustering. Stomatal frequencies were similar in specimens from
each Alberta dune, but some VE characters were variable. These
structural data were compared to those of S. planifolia ssp.
tyrrellii from the Athabasca sand dunes in Saskatchewan.
Similarities among values of adaxial stomatal frequency between
specimens from Alberta and Saskatchewan suggest adaptation to this
high light intensity environment. Overall, structural similarities
described in this study provide additional support for the close
taxonomic relationship of this endemic-progenitor Salix pair.
Key words: Athabasca sand dunes, Salix, stomata, structure, vessel element, willow