Selaginella

Selaginella is the sole genus of vascular plants in the family Selaginellaceae, the spikemosses or lesser clubmosses. This family is placed in the class Isoetopsida, distinguished from the sister group Lycopodiopsida by having scale-leaves bearing a ligule and by having spores of two types. They are sometimes included in an informal paraphyletic group called the "fern allies". S. moellendorffii is an important model organism. Its genome has been sequenced by the United States Department of Energy's Joint Genome Institute.

Characteristics

Selaginella species are creeping or ascendant plants with simple, scale-like leaves (microphylls) 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. Under dry conditions, some species of Selaginella roll into brown balls (a phenomenon known as poikilohydry). In this state, they may be uprooted. Under moist conditions the brown balls become green, because of which these are also known as resurrection plants (as in Selaginella bryopteris).