Mosses are small flowerless plants that typically grow in dense green clumps or mats. The individual plants are usually composed of simple leaves that are generally only one cell thick, attached to a stem that may be branched or unbranched and has only a limited role in conducting water and nutrients. Mosses for practical purposes here include hornworts and liverworts. Different moss species include Vesicularia, Fontinalis, Tortula, Fissidens, Taxiphyllum, Pellia, Riccia, Plagiochilaceae and more.