Equisetum

Lore & Background

Equisetum species are perennial herbaceous plants that die back in winter in most temperate species or are evergreen in most tropical species and a few temperate ones. myriochaetum can exceed 8 m. Their leaves are greatly reduced, non-photosynthetic, and arranged in whorls fused into nodal sheaths; the stems are hollow, jointed, and ridged, and are the main photosynthetic organs. Spores are produced in cone-like strobili at the tips of some stems. Most species are homosporous, though field horsetail produces smaller spores that give rise to male prothalli. The spores have four elaters that assist dispersal through crawling and hopping motions after the sporangia split open. Spores are photosynthetic and typically live up to two weeks, germinating immediately under humid conditions. Equisetum cell walls contain mixed-linkage glucan (MLG), a polysaccharide otherwise known only in the Poales, and a novel enzyme called mixed-linkage glucan : xyloglucan endotransglucosylase (MXE), not found in any other plants. The evolutionary distance between Equisetum and Poales suggests each evolved MLG independently.

Reader's Guide

Equisetum holds significant evolutionary importance as a living fossil, representing the only surviving genus of the subclass Equisetidae, which dominated the understorey of late Paleozoic forests for over 100 million years. Its ancient relatives, such as the tree-sized Calamites, are abundant in Carboniferous coal deposits. The genus first appears in the Early Jurassic, with fossils like E. dimorphum from Patagonia and E. laterale from Australia showing modern morphological features. Today, Equisetum species are near-cosmopolitan and are considered weeds or invasive in some areas. They are toxic due to thiaminase content but have been used as food and in folk medicine. The genus is divided into three subgenera—Equisetum, Hippochaete, and Paramochaete—with 18 accepted species. Hybrids occur only within the same subgenus. The discovery of MXE enzyme and MLG in Equisetum cell walls highlights its unique biochemistry, distinct from other land plants, and provides insight into the evolution of cell wall modification mechanisms.

Did You Know?

• Equisetum is the only living genus in Equisetaceae and reproduces by spores rather than seeds.
• The oldest remains of modern Equisetum species first appear in the Early Jurassic.
• Equisetum cell walls contain mixed-linkage glucan (MLG), a polysaccharide otherwise known only in the Poales.
• The genus contains a novel enzyme, mixed-linkage glucan : xyloglucan endotransglucosylase (MXE), not found in any other plants.