At least thirteen taxa of bryophytes occur between 40 and 128 m depth in Waldo Lake, Oregon. Many taxa exhibit morphological modification precluding positive identification below the level of genus. Liverworts comprise about 98% of the bryomass, the balance being pleurocarpous mosses with trace representation of acrocarps. Predominance of liverworts at extreme depth suggests that they are more viable than mosses under attenuated blue light. All liverworts except one are apparently aquatic forms of upland species. Two mosses are normally upland species, the rest aquatic. Red pigments in some liverwort taxa were maintained as deep as 70 m, but most lost pigment below 40 to 50 m.Sphagnummaintained red pigment as deep as 100 m. Although production of benthic plants would be expected to be exceedingly slow under conditions of low light, low temperatures, limited nutrient availability, and considerable hydrostatic pressure, new growth of 1.5 to 3 cm on liverwort stems approximates annual growth increments observed on upland plants.