This densely cespitose, short-culmed species has been confused with tonsa (or rugosperma), and both taxa have been often overlooked due to their low hidden inflorescences (with staminate spikes often lacking pistillate spikes on same culm). In Ky. and elsewhere umbellata appears to be typical of relatively base-rich soils in dry open woods and grasslands, "often at edges of ant hills" (FNA 23). However, it is variable across its range, and some populations may occur in more acid or sandy soils (e.g. Y); 2n = 30 and 32. See also notes under reznicekii.