Clubmosses are thought to be structurally similar to the earliest vascular plants, with small, scale-like leaves, homosporous spores borne in sporangia at the bases of the leaves, branching stems (usually dichotomous), and generally simple form.
Lycopodiaceae, as narrowly defined, comprises the extant genus, Lycopodium, which includes the Wolf's-foot clubmoss, Lycopodium clavatum, Ground-pine, Lycopodium obscurum, Southern ground-cedar, Lycopodium digitatum, and other species. Also included are species of Lycopodiella, such as the Bog clubmoss, Lycopodiella inundata. Most of the Lycopodium favor acidic, sandy, upland sites, whereas most of the Lycopodiella favor acidic, boggy sites.
The other major group, the Family Huperziaceae, are known as the firmosses. This group includes the genus Huperzia, such as the Shining firmoss, Huperzia lucidula, the Rock firmoss, Huperzia porophila, and the Northern firmoss, Huperzia selago. This group also includes the odd, tuberous Australasian 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.
A powder known simply as lycopodium, consisting of dried spores of the common clubmoss, was used in Victorian theater to produce flame-effects. A blown cloud of spores burned rapidly and brightly, but with little heat. It was considered safe by the standards of the time.