Isoetes minima was described from a single collection made by Wilhelm Suksdorf from Spangle near Spokane, WA, and until recently, the only authentic material of this taxon has been the type specimen. On the same collecting trip, Suksdorf collected copious material of Isoetes howellii that looked superficially the same as the type of I. minima. Based on this limited material, N.E. Pfeiffer reduced I. minima into a variety of I. howellii. The Flora of North America followed Pfeiffer and redefined this variety to include any small plants of I. howellii with small megaspores. Several years ago, we found several large populations of I. minima in Wenatchee Mountains, WA, and in 1996 this species was also found in south-central British Columbia. Isoetes minima differs from I. howellii by having small, spiny megaspores and by sporangia that completely lack velum. Ecologically, I. minima occupies the most extreme habitats among the western North American terrestrial Isoetes species. It grows in periodically wet depressions in Artemisia tridentata sagebrush with Hesperichon pumilus, Lewisia pygmea, and Floerkea proserpinacoides as accompanying species.

Key words: Isoetes minima, Pacific Northwest, Pteridophyta