THOMPSON, JONATHAN E. AND SUSAN R. KEPHART.* Department of Biology, Willamette University, Salem, OR 97301. - Varietal and species relationships of the Silene douglasii complex as delimited by pollen ultrastructure.
Systematists use a broad range of evidence to construct
classifications. Micromorphological characters such as pollen and
seeds can be used to reevaluate phylogenetic and cladistic
relationships based on macromorphology. However, among close
relatives within a genus, micromorphological differences are often
slight. We examined ultrastructural features of 15 species or
varieties in the genus Silene L. (Caryophyllaceae), as a means
of evaluating relationships within the proposed S. douglasii
complex. Approximately 10% of the silenes known worldwide occur
within North America, and are characterized by polyporate pollen. We
detected significant differences among species for both quantitative
and meristic characters of the pollen (e.g., grain and pore size, pore
number), and used these for phenetic and cladistic analyses. Pollen
grains ranged in size from 35.25 ± 0.98 µm for S. parryi to
31.53 ± 0.39 µm for S. spaldingii, which also had the largest
number of pores. Surprisingly, we also detected differences in pollen
surface ornamentation among varieties of S. douglasii Hook,
which falls within the same clade as S. parryi, and whose
position relative to S. parryi had previously been disputed.
Key words: Caryophyllaceae, micromorphology, pollen, Silene, ultrastructure