The genus Selaginella is classified in the division Lycophyta, which includes the numerous plants commonly known as clubmosses and spike mosses. Similar to their close relatives, Selaginella plants develop strobili, spike-like reproductive organs that form on fertile branches. Selaginella are unique, however, from other lycophytes in that their strobili contain two different types of spores. The spore cases near the bottom of a vertical strobilus have a lumpy appearance and are generally lighter in color than the sporangia near the apex of the structure. Within each of the basal spore cases are only four spores, but these spores, termed megaspores, are quite large. They develop from the meiosis of a single sporocyte. In contrast, the apical spore cases exhibit a smooth oval form and each contain numerous very small spores referred to as microspores that are produced by multiple sporocytes.