Flora of North America species comparison

Reports of Saxifraga hyperborea from Mount Washington, New Hampshire (e.g., Á. Löve and D. Löve 1964) require confirmation; all specimens examined from this location appear to be S. rivularis. C. L. Hitchcock (1961) treated all western material as S. debilis, including that of the Pacific Northwest that is included here. For Colorado, W. A. Weber (1990) appears to have applied the name S. rivularis to what we call S. hyperborea, and S. hyperborea subsp. debilis to what we call S. debilis. P. K. Holmgren and N. H. Holmgren (1997) included under their broad concept of S. rivularis both S. hyperborea and S. debilis, noting that the plants had gone usually under the latter name. Both species are present in the Rockies and the Intermountain Region.

In northeastern North America, Saxifraga hyperborea and S. rivularis are often sympatric, although the latter is absent from the extreme north. The major distinguishing feature between diploid S. hyperborea and tetraploid S. rivularis is the presence of rhizomes in the former and their absence in the latter (see key), a character that is sometimes difficult to interpret on herbarium sheets. Plants of S. hyperborea are usually smaller (2–5 cm) and reddish (sometimes green), with usually three- to five-lobed leaves and petals about one and one-half times longer than sepals, while plants of S. rivularis are taller (5–10 cm) and usually green (although sometimes reddish, particularly in the western var. arctolitoralis), with usually five-lobed leaves and petals two to three times longer than sepals.

(Discussion copyrighted by Flora of North America; reprinted with permission.)