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 Ám for S. parryi to 31.53 ▒ 0.39 Ám 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