Lycopodiophyta is a division of seedless vascular plants best known as clubmosses and quillworts. The plants are relatively small, and are herbaceous. They usually have branched stems and small leaves, but their fossil ancestors were trees. Lycopodiophyta have three main groups but are subdivided at the class level. These three separate classes are the lycopodiopsida, selaginellopsida and class isoetopsida.
This plant has a grass-like appearance and are therefore not readily identified. Yet they are most commonly the size of a small tree. It is a vascular and herbaceous plant. It has an epidermis, cortex, and a stele, or central cylinder, of conducting tissue. The sporangia, or the spore cases, are usually borne at the base of the leaf. They are either clustered into a terminal cone, or strobilus, or they are scattered along the stem. They are unique from all other vascular plants because they have microphylls which are leaves that have a single vein, other than the more complex ones that are usually found in ferns and seed plants.
When the plant hits maturity, the sporangia splits across the top. It then releases large amounts of spores. The spores that are released germinate, and then produce fleshy, small, non-green gametophytes. The gametophytes bear both sperm-producing antheridia, and egg-producing archegonia. The sperms that are motile swim and make their way to the egg. When they swim, they go through a film of water. The zygote, or fertilized egg, gives rise to an embryo and eventually leads to a mature sporophyte.
During the Silurian and Devonian periods according to the evolutionary geologic column, this species of plants were among the first to adapt towards the land. The ocean currents blended water, oxygen, and nutrients into a soup, while the land, a structure that was layered with water and other minerals in the soil, and light and oxygen in the air. The risk of genetic damage got bigger as the intense sunlight was presented. Without water, more structural support was required to resist gravity, and pervasive desiccation became a possibility. During the Carboniferous period, huge forests were formed by the tree-like Lycopodiophyta.