Division

• Spike moss plants are in the kingdom Plantae. Their division is with the club mosses in the group Lycophyta. Lycophytes are some of the oldest vascular plants and have been on the earth for 40 million years. Lycophytes grow a modified leaf called a mycrophyll, which has one single vein in it that is part of the vascular system. Spike mosses have lost the mycrophyll in evolutionary processes, but the leaf structure is otherwise the same.
  
  

Family

• Sellaginellaceae is the family group to which spike mosses belong. The plants are either terrestrial or epiphytic or vertically located. These mosses have a rhizome and and leaves that have a tiny basal flap on the end called a ligule. Sellaginellaceae have two types of spores; megasporangia and microsporangia develop the female and male gametophytes respectively. Microspores burst and release sperm which must travel through water to reach the ovule created by the megasporangia. Sellaginellaceae are nonflowering plants with aquatic tendencies.
  
  

Tribe

• Spike moss belongs to the Senecioneae. This tribe is characterized by a cluster of lightly hairy bracts or modified leaves. Each bract is joined to the next to come together at the core of the plant. The majority of the bracts are the same size and length, with the exception of a few smaller ones at the base of the plant. The bracts may radiate out from the center of the plant or may circulate it in the form of a disc.
  
  

Genus

• Spike moss is classified as being of the genus Selaginella. These mosses are all related to the club mosses and are found clinging to rocks and nestled on trees. The subgenera are Selaginella, Tetragonostachys and Stachygynandrum, with possibly a fourth and fifth subspecies. The plants have different side leaves called upperside leaves, and also carry underside leaves borne on the side closest to the surface of the plant's axis.