Notes: FNA8: "Classification of Saxifragaceae has been varied and controversial (e.g., A. Cronquist 1981; H. G. A. Engler 1930; J. Hutchinson 1973; G. K. W. Schulze-Menz 1964b; A. L. Takhtajan 1997; R. F. Thorne 1992). Molecular phylogenetic data (D. R. Morgan and D. E. Soltis 1993; Soltis et al. 1993, 2001; Angiosperm Phylogeny Group 1998, 2003) reveal that genera of Saxifragaceae in the broad sense are allied with at least ten separate, often distantly related families of flowering plants. These data also suggest that Saxifragaceae in the narrow sense as treated here consists of about 38 genera worldwide, equivalent to subfamily Saxifragoideae, one of the 15 subfamilies recognized by Engler and one of the 17 recognized by Schulze-Menz of the broadly defined Saxifragaceae. Molecular phylogenetic data (Soltis et al. 2001) show that the narrowly defined Saxifragaceae fall into two major groups: Saxifraga, and the heucheroid clade encompassing all other genera. Molecular data further show that Saxifraga, as traditionally understood, is polyphyletic, comprising two distinct lineages (treated here as Saxifraga and Micranthes) and the monospecific North American Cascadia. The major split between Saxifraga and the heucheroid clade is supported not only by molecular data from six DNA regions but by differences in patterns of floral morphology. Saxifraga has a relatively uniform floral morphology (radially symmetric flowers, with bilateral symmetry restricted to one Asian group of species, which consistently have the same number of sepals, petals, stamens, and carpels). Almost all of the variation in the family in numbers of sepals, petals, stamens, and carpels occurs in the heucheroid clade. Radially symmetric flowers predominate there, but some bilateral flowers are found in Bensoniella, Micranthes, Tolmiea, and some species of Heuchera."
NOTE: Past and contemporary research have indicated that Mitella is a polyphyletic group best treated as multiple genera. The treatment here reflects that view, which is also consistent with how these taxa were treated by Abrams in "Illustrated Flora of the Pacific States".
FNA8: "Mitella is treated here in the broad sense; phylogenetic data indicate that it is polyphyletic (D. E. Soltis et al. 1990; Soltis and R. K. Kuzoff 1995). Historically, four or five genera have been recognized (including Mitella, Ozomelis Rafinesque, Pectiantia Rafinesque). Formal restructuring of generic boundaries is complicated by the presence of nearly a dozen Asian species (M. Wakabayashi 2001) and lack of a comprehensive understanding of the genus relative to the rest of Saxifragaceae. Mitella nuda and M. diphylla, both with ten stamens, form a clade that would comprise a narrowly defined Mitella. A second clade composed of M. diversifolia, M. stauropetala, M. trifida, and Conimitella williamsii would form a second, distinct genus. Molecular data suggest that M. breweri, M. caulescens, and M. pentandra also form a distinct clade and perhaps a third, distinct genus. The relationships of M. ovalis are less certain; some analyses suggest that it may be sister to the genus Tolmiea (Soltis and Kuzoff; Kuzoff and Soltis, unpubl.)."
Family information last updated 5/23/2019 by David Giblin.