[intermountainbiota.org] Taxonomy History: Johnson placed Saxifraga nuttallii in his monotypic genus Cascadia based on the unusual habit, free carpels, and spiny seeds. Molecular phylogenetic data (M. E. Mort and D. E. Soltis 1999; Soltis et al. 2001) placed Cascadia as sister to the southern South American (Tierra del Fuego) Saxifragodes D. M. Moore, both sister to Micranthes. Mort and Soltis considered the ovary of Cascadia to be superior because the two carpels are distinct to their bases; the hypanthium, fused to each carpel, gives the ovaries a semi-inferior appearance. Ovules in Cascadia are bitegmic, as in Saxifraga; those of Micranthes are usually unitegmic. (link added by Mary Ann Machi)