Phylogenetic Relationships Within Lithophragma (Saxifragaceae): Hybridization, Allopolyploidy, and Ovary Diversification

Abstract

We explore phylogenetic relationships in Lithophragma through parsimony and maximum like- lihood estimation analyses of internal transcribed spacer sequences of 18S-26S ribosomal DNA. Results based on internal transcribed spacer sequences are compared with those from previous studies based on chloroplast DNA restriction site, morphological, and flavonoid variation. Phylogenetic analysis of internal transcribed spacer sequences produces a highly resolved topology with six main clades. These results suggest that three previously described species of Lithophragma are not monophyletic. Based on this topology and previous findings, two species not recognized in the most recent monograph, L. thompsonii and tetraploid L. bolanderi, are hypothesized to have arisen through hybridization and allopolyploidy, respectively. Flowers of Lithophrag- ma exhibit a diverse array of ovary positions ranging from what has been described as superior to deeply inferior. Analysis of ovary position in light of our phylogenetic results reveals a complex pattern of diversi- fication in Lithophragma. This pattern is explored through character mapping and correlation analyses and is found to be inconsistent with either an active or a passive trend toward greater inferiority. A weak relation- ship between variation in ovary position and the topological position of each taxon suggests homoplastic