Equisetaceae

Equisetaceae is a family of vascular plants in the order Equisetales. It contains a single living genus, Equisetum, whose species are commonly known as horsetails or scouring rushes. There are about 15 described species, distributed worldwide, and they are typically divided into two subgenera: Equisetum and Hippochaete. The group has an extensive fossil record and is one of the surviving lineages of a once-diverse Paleozoic flora.

Members of Equisetaceae are perennial, herbaceous plants with hollow, jointed stems that can resemble bamboo. Stems are often ridged and silica-rich, and leaves are reduced to small scales at the nodes. Whorled branches emerge from the nodes, giving a brushlike appearance. The sporophyte is the dominant phase of the life cycle and produces spores in terminal strobili on fertile shoots; spores germinate into a free-living gametophyte. Fertilization requires water for the motile sperm.

Ecology and distribution: Equisetum species occur in damp habitats worldwide, including wetlands, stream banks, and disturbed soils. Some species tolerate drier conditions or transient water, and many spread vegetatively via underground rhizomes and tubers.

Fossil and evolutionary context: The Equisetaceae have a rich fossil history, with ancient relatives reaching great size during the Carboniferous and Permian periods. Modern Equisetum species are the sole living representatives of this once-diverse lineage and are often cited as indicators of ancient plant groups in paleobotany.

Uses and interactions: Humans have historically used horsetails for their high silica content in scouring and polishing, and the plants appear in traditional medicine. In horticulture, some species are grown as ornamentals, though they can be invasive in suitable environments and are not considered edible.