Phylum including three living families. This is an ancient lineage with fossil members dating from the Devonian.
Vegetative Characters: Plants with true leaves, roots and stems -link to an illustration- . Leaves are, without exception, microphylls and this is a defining feature of the group (hence, the alternate name for the phylum - the Microphyllophyta). Microphylls have only one vein and are not associated with a leaf gap. They are thought not to be homologous to macrophylls found in ferns and all the groups of seed plants. Roots are adventitious. Branching in both shoot and root occurs by the division of the apical meristem into two parts which can either be equal or with one subordinate and one superior branch. Living members are all herbaceous although Isoetes has secondary growth. Extinct members include tree-like plants which were a prominent part of the Carboniferous swamp-forests and are well represented in the fossil record.
Reproductive Characters: Non-seed plants which are either homosporous with exosporic gametophytes or heterosporous with endosporic gametophytes.
Vegetative Characters: Leaves have ligules and are typically arranged in four rows along the stem. Two rows have short leaves and the other two with long. Shoot is flattened with distinct ventral and dorsal sides.
Reproductive Characters:Heterosporous with endosporic gametophytes. Spores are borne on sporophylls which are always arranged into strobili. Typically megasporophylls and microsporophylls are found together in the same strobius.