The stems have very well defined nodes and internodes 4. Internally the stems have a central hollow pith surrounded by a ring of smaller canals. Each of the smaller canals is associated with a strand of primary xylem and primary phloem 5. The leaves are very reduced to scales, which are interpreted as being reduced megaphylls 6. Strobili may be borne at the tips of a vegetative axis, or borne on a non-chlorophyllous fertile branch that develops from the rhizome 7.
Gametophytes are green and free living.
They may be either bisexual or male. In bisexual ones the archegonia develop before the antheridia to ensure outcrossing 8.