Mosses are plants with a simple body structure (Figs. 3.1, 3.2, 3.3, 3.4, 3.5, and 3.6). Their living species today are classified into the liverworts, mosses, and hornworts phyla. They do not have real organs, some of their leaves are often only one cell layer thick. Most of their species are a few centimetres in size. The moss plant (gametophyte) is a plate-like colony or a small shoot-like body consisting of a stem and leaves, which is anchored to the substrate by root-like filaments.