|Spike mosses mainly have a tropical distribution, growing in moist shaded habitats, aithough a few are found in deserts. They are terrestrial, perennial or annual plants, without true roots. The stems are usually branched, with small simple leaves that are arranged in four rows, with two rows having long leaves, and two with small leaves. A small outgrowth called ligule is located on the upper surface of each leaf, close to where it joins the stem.
These plants are heterosporous, that is it reproduces through two type of spore. Sporangia are borne by specialised leaves called sporophylls, which are usually aggregated into strobili. Microsporangia produce many microspores, which germinate to form short-lived microgametophytes that produce sperm. Megasporangia produce a few larger megaspores each, and these form megagametophytes that produce eggs in specialised organs called archegonia. To reach an archegonium and fertilise an egg, a sperm cell must swim in a film of water.
New Zealand has no native species in the Selaginellaceae family. Unfortunately one species Selaginella kraussiana has been introduced and has become naturalised. It can be found in lowland forest in the North Island along walking tracks, and beside streams. It's a serious nuisance in many places, pushing out native species.