Horsetails are a group of tracheophytes that are characterized by stems and rhizomes that have ridges and furrows. In the stem are contained carinal and vallecular canals. The carinal canal is smaller of the two and is associated with the vascular bundle and is opposite the ridges of the stem and rhizome. The vallecular canal is opposite the furrows. Horsetails are in the division Sphenophyta and have only one genus, Equisetum. These plants are typically found in damp to wet habitats.