Sphenopsida is a class of vascular plants that includes the group commonly known as horsetails. These plants are characterized by their jointed stems, whorled leaves, and a distinctive appearance that resembles ancient plants. They thrive in wet environments and are often found in marshes and along riverbanks. Horsetails reproduce using spores rather than seeds, and they have a unique life cycle that includes both a sporophyte and a gametophyte stage. Sphenopsida is considered a primitive group of plants, with a lineage that dates back to the Paleozoic era, making them one of the oldest surviving plant groups on Earth.