A PHYLOGENETIC ANALYSIS OF BESSEYA (SCROPHULARIACEAE)

Phylogenetic relationships among species of Besseya (Scrophulariaceae) were examined using cladistic analysis of morphological characters. A single most parsimonious tree was discovered on which B. bullii, loca ted in central North America, was placed as the sister species of the rest of the genus, making up taxa of the Rocky Mountains and the Pacif ic Northwest. Among the species in the Rocky Mountain and Pacific Nort hwest group are B. rubra and B. wyomingensis, both of which have flowe rs that are characterized by extreme corolla diminution. Besseya rubra and B. wyomingensis did not form a monophyletic group on the most par simonious cladogram. Topologies on which B. rubra and B. wyomingensis were placed as a monophyletic group required at least two character st ate changes more than the most parsimonious cladogram. Alternative sce narios for corolla evolution were possible based on the most parsimoni ous cladogram. One scenario indicated that the extreme corolla diminut ion characteristic of B. rubra and B. wyomingensis occurred once and t hat an evolutionary reversal reestablished the full-size corolla of so uthern Rocky Mountain species. A second scenario, for which the hypoth esis of an evolutionary reversal was not required to explain the full- size corolla of the southern Rocky Mountain species, indicated that ex treme corolla diminution occurred separately in the evolution of both B. rubra and B. wyomingensis. Sympetaly, generally considered a highly conserved attribute among angiosperms, was diminished within Besseya through the loss of a corolla tube in the southern Rocky Mountain spec ies. In the evolution of Besseya, especially in association with the o rigin of the monophyletic group consisting of B. oblongifolia, B. plan taginea, and B. ritteriana, leaf lamina length/width ratios greatly in creased, lamina bases became less cordate, and basal secondary vein di ameter/midvein diameter ratios decreased.