Equisetum
Equisetum is the sole living genus of horsetails, a group of vascular plants with jointed, silica-rich stems and spores borne in cone-like structures.
Vascular plant: A plant with specialized tissues that transport water, minerals, and sugars through its body. Equisetum has vascular tissues despite lacking flowers and seeds.
Node (botany): A point on a plant stem where leaves, branches, or buds arise. Horsetail stems are visibly divided into nodes and intervening internodes.
Common horsetail: Equisetum arvense, a widespread horsetail with separate fertile and sterile shoots. Its distinct shoot types illustrate the seasonal variation found within the genus.
Herbal medicine: The use of plants or plant-derived preparations to prevent or treat health conditions. Preparations of Equisetum arvense have a history of medicinal use, though evidence and safety vary.
Ferns: A group of vascular plants that reproduce by spores and typically have divided fronds. Like ferns, horsetails are seedless vascular plants, but their stems and reproductive structures differ.
Sporophyte: The diploid, spore-producing stage in the life cycle of plants and many algae. The conspicuous horsetail plant is the sporophyte, which produces spores in strobili.
Internode: The section of a plant stem between two successive nodes. Hollow, ridged internodes give horsetail shoots their segmented appearance.
Rough horsetail: Equisetum hyemale, a stiff, evergreen horsetail with prominent silica deposits in its stems. Its rough stems show why some horsetails were used for scouring and polishing.
Diatomaceous earth: A soft sedimentary material composed mainly of fossilized diatom silica shells. Both it and horsetail stems are abrasive because they contain silica, but their origins differ.
Lycophyte: A lineage of vascular plants that includes clubmosses, spike mosses, and quillworts. Lycophytes are another ancient seedless lineage, separate from the horsetail lineage.