The Class Lycopsida is a group of vascular plants that evolved during the Devonian period and were once a dominant group of plants on Earth. This class is also commonly referred to as the Lycopodiophyta, or Lycopsids for short. Other synonyms for this plant class include Lycopodiales, Club Mosses, Ground Pines, and Selaginellales. These names highlight the common features of these plants, which include small leaves and stems that are often arranged in spikes or cones. Despite their small size, these plants were important constituents of ancient forests and played a key role in the evolution of Earth's ecosystems.