Selaginella densa, small clubmoss, is an important component of central Montana foothill grasslands. In an area where it occupied 10—20% of the soil surface, above—ground biomass was 42—101 g/m². Soils growing S. densa were shallower, more rocky or gravelly, but less sandy, than soils without this species. High levels of fertility, shading and mulch reduced, but additional water increased, its cover. Contrary to other reports, we found a greater decrease in cover on areas grazed intensively than on areas protected for 4 years. Cover on moderately grazed sites or on adjacent protected areas did not change.