The chloroplasts of some hornworts and algae contain structures called pyrenoids. They include mosses, liverworts and hornworts. Typical submerged plants are Charales, pond weed, hornworts and water lilies. In the bryophytes, including liverworts, hornworts and mosses, sex chromosomes are common. Mosses are commonly confused with hornworts, liverworts and lichens. The three living divisions are the mosses (Bryophyta), hornworts (Anthocerotophyta), and liverworts (Marchantiophyta). Megaceros is a genus of hornworts in the family Dendrocerotaceae. All other hornworts remain in the class Anthocerotopsida. The bryophytes, which include liverworts, hornworts and mosses, reproduce both sexually and vegetatively. Pyrenoids in algae and hornworts also act to concentrate around RuBisCO. In the bryophytes (liverworts, mosses and hornworts), the sexual gametophyte is the dominant generation. Protonema are characteristic of all mosses and some liverworts but are absent from hornworts. Liverworts, mosses and hornworts spend most of their lives as gametophytes. Bryophyta (mosses) and Anthocerotophyta (hornworts). "Nostoc commune" can occur in pockets in the thallus of hornworts such as "Phaeoceros".