BUECHLER, WALTER K. Boise, ID 83705. - Estimating polyploidy levels from cell size in Salix leaves.
Leaf material from 41 herbarium specimens representing 31 Salix taxa
was examined for correlation between polyploidy levels and size of
petiole epidermal cells and stomatal guard cells. The species included
most of the polyploidy levels encountered in contemporary Salix (2n =
38, 76, 114, 152, 190). Petiole epidermal cell size allowed a clear
distinction between diploids and tetraploids. The same was true for
guard cell size if comparisons were made only within sections or
within groups of closely related sections. Polyploidy levels higher
than tetraploid could be estimated to +/- 2 - 4x. The data suggest
that cell size may depend also, to a minor degree, on climate. Some
cultivars that were transplanted from high to lower altitudes showed
exceptionally large cell sizes; such specimens should be excluded from
reference data. Contrary to chromosome counts where live material is
necessary, these cell size methods can be used on herbarium material
and on well-preserved fossil specimens (the epidermis of the petiole
is often the only organically preserved part of a leaf remain). Cell
size methods are also suitable to scan large numbers of living plants
for deviations in chromosome numbers, because preparation and
measuring procedures are relatively simple. The petiole cell size
method was applied to 14 fossil Salix leaves from the Late Miocene
Pickett Creek flora (Idaho). Salix succorensis Chaney and Axelrod, S.
inquirenda Knowlton, S. wildcatensis Axelrod, S. desatoyana Axelrod,
and two undetermined specimens were found to be diploid. The result
for S. wildcatensis is of particular interest because its closest
modern relative, S. lasiolepis Benth., is tetraploid. The objective of
future studies is to estimate the age of some polyploid complexes in
Salix by fossil evidence.
Key words: cell size, guard cell, Miocene, polyploidy, Salix, stoma