Spikemoss refers to any plant of the genus Selaginella in the family Selaginellaceae. Many workers still place the Selaginellales in the class Lycopsida (modern nomenclature: Lycopodiopsida). This group of plants is included in what, for convenience, is called "fern allies".
The spikemosses are creeping or ascendant plants with simple, scale-like leaves on branching stems from which roots also arise. The plants are heterosporous (megaspores and microspores), and have structures called ligules, scale-like outgrowths near the base of the upper surface of each microphyll and sporophyll.
Unusually for the lycopods, each microphyll contains a branching vascular trace.
There are about 700 species of Selaginella, showing a wide range of characters; the genus is overdue for a revision which might include subdivision into several genera. Better-known spikemosses include:
Many species of Selaginella are desert plants known as "resurrection plants", because they curl up in a tight, brown or reddish ball during dry times, and uncurl and turn green in the presence of moisture. Other species are tropical forest plants that appear at first glance to be ferns.