Lycopsida

A clubmoss is one of a group of plants in the order Lycopodiales, in the class Lycopsida. These plants are often loosely grouped in the fern ally category. They are thought to be structurally similar to the earliest vascular plants, with small, scale-like leaves, homosporous spore borne in sporangia at the bases of the leaves, branching stems (usually dichotomous), and generally simple form.

There are two major groups of clubmosses, which some now may even consider to be different families, although they were once all included in the genus Lycopodium. One group includes the modern version of the genus Lycopodium, which in turn includes such species as the wolf's-foot clubmoss, Lycopodium clavatum, ground-pine, Lycopodium obscurum, and southern ground-cedar, Lycopodium digitatum and other species; and Lycopodiella, including such species as the bog clubmoss, Lycopodiella inundata. Most of the Lycopodium genus favor acid, sandy, upland sites, while most of the Lycopodiella genus favor acid, boggy sites.

The other major group is often termed the firmosses. This includes the genus Huperzia, which in turn includes such species as the shining firmoss, Huperzia lucidula, the rock firmoss, Huperzia porophila, and the northern firmoss, Huperzia selago. This group also includes the odd tuberous Australian plant Phylloglossum which was, until recently, thought to be only remotely related to the clubmosses. However, recent genetic testing has shown it to be very closely related to the genus Huperzia.

Also see spikemoss and quillwort.