High resolution light microscope images and detailed descriptions of valve metrics and valve morphology are provided for about 60 species of Cymbellafalsa, Cymbopleura and
Delicatophycus from western North America. Three new species are described—Cymbopleura inuitorum, C. montana and C. navicularis—and seven new names, combinations and changes in status are proposed. For most species, images are from multiple populations and populations are often represented by multiple specimens representing entire life cycles. The three genera are
typically found in cold, oligotrophic and somewhat alkaline waters with low to moderate conductivity, and at northern latitudes, in the mountains, or at lower elevations that have been
glaciated. The southern range limit for several of these cold-water stenothermal taxa is in the mountains of the Northwest United States near the border with Canada (49° N latitude), where they are at risk of extirpation due to climate change. Most of the taxa recorded from western North America are also found in Eurasia, supporting the concept of a Holarctic kingdom of diatoms.