Gymnostomum tetragonum Bridel, Muscol. Recent., suppl. 1: 270. 1806

Plants scattered to gregarious; leaves with arcuate acumen when dry, capsules hidden in large angular calyptrae.

Capsules mature Jan-May. Mineral soil, grasslands, less often forests, river banks, commonly among other mosses; mainly moderate elevations; Iowa, Kans., Minn., Mo., Nebr., N.Mex., Okla., Tex.; n, c Europe, n Africa.

Pyramidula tetragona is easily identified by the large, four-angled calyptra that encloses virtually the entire sporophyte. The capsule that sharply contracts to the neck, which itself is abruptly narrowed to the seta, also distinguishes the species. In addition, no other species of Funariaceae produces rhizoidal tubers.