Title: A Phylogenetic Analysis of Besseya (Scrophulariaceae)
Abstract: 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, located 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 Pacific Northwest. Among the species in the Rocky Mountain and Pacific Northwest group are B. rubra and B. wyomingensis, both of which have flowers that are characterized by extreme corolla diminution. Besseya rubra and B. wyomingensis did not form a monophyletic group on the most parsimonious cladogram. Topologies on which B. rubra and B. wyomingensis were placed as a monophyletic group required at least two character state changes more than the most parsimonious cladogram. Alternative scenarios for corolla evolution were possible based on the most parsimonious cladogram. One scenario indicated that the extreme corolla diminution characteristic of B. rubra and B. wyomingensis occurred once and that an evolutionary reversal reestablished the full-size corolla of southern Rocky Mountain species. A second scenario, for which the hypothesis of an evolutionary reversal was not required to explain the full-size corolla of the southern Rocky Mountain species, indicated that extreme 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 species. In the evolution of Besseya, especially in association with the origin of the monophyletic group consisting of B. oblongifolia, B. plantaginea, and B. ritteriana, leaf lamina length/width ratios greatly increased, lamina bases became less cordate, and basal secondary vein diameter/midvein diameter ratios decreased.
Publication Year: 1993
Publication Date: 1993-06-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 7
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