This is a highly variable near-cosmopolitan species, usually associated with small or shallow ephemeral pools, drawdown shores and similar sites. Taxonomic segregates have not yet been well defined; 2n = 26 to 120 (Cr, FNA 22). J. bufonius is the only strictly annual species of Juncus known in eastern North America. It is often confused with tenuis and allied species in Ky., thus relatively undercollected. Determination of annual habit can be difficult. J. bufonius also differs in its relatively long inflorescences: ca. 25-90% of plant height versus 15-30% in most tenuis or allies. Also, leaf sheaths gradually taper to the summit without an auricle (versus auricled or prolonged above blade base).