Bio-indicators are physiological, chemical, or behavioral changes that occur in organisms as a result of changes in the environment. Bryophytes of the genus Hypnum are particularly sensitive to pollutants, especially sulfur dioxide. As a result, most bryophytes are not found in cities and industrial areas. Mosses and liverworts, especially Hypnum cupressiforme and Homalotecium serieceum, have also been used as bio-indicators—one example was to monitor radioactive fallout from the Chernobyl nuclear reactor accident in 1986.

Hornworts are more closely related to green algae than to any other group of plants. Hornwort cells usually have a single, large chloroplast with a granular, starch-containing body (pyrenoid) similar to those in green algae. Mosses and liverworts are like all other plants because they have many dish-shaped chloroplasts per cell.