The taxonomy of Cinclidium, with only four species recognized, has been remarkably stable compared to most other genera in the Mniaceae. Two bisexual diploids (C. stygium and C. subrotundum) with n = 14 and two unisexual haploids (C. arcticum and C. latifolium) with n = 7 have been accepted since 1877, when C. latifolium was the last of these to be described. In the course of our inquiries into the nature of polyploidy in the genus, we discovered a new, genetically distinct species that has previously been mistakenly referred to C. latifolium and which we originally assumed was C. subrotundum. Cinclidium alaskanum is also morphologically distinct from the other four species, occupies distinctive microhabitats on the North Slope of Alaska, and is unisexual and haploid with n = 7.