Field horsetail (Equisetum arvense) is the most common species of Equisetum. The popular and widely used name "horsetail" comes from the Latin words equus (horse) and seta (bristle), from the peculiar bristly appearance of the jointed stems of the plants. Its relatives, some of which were 100 feet tall, dominated the understory of the late Paleozoic forests nearly three hundred million years ago. This group of non-flowering plants reproduces from spores, not seeds, and is closely related to ferns. Field horsetail has both fertile and vegetative stems. The fertile (tan), short-lived stem terminates in a spore-bearing cone. The vegetative stem bears whorls of green leaves.