Equise�tum, a genus of vascular cryptogamous plants with hollow jointed stems, type of the group Equisetales, growing in wet places, and popularly called horse-tails.

The available data, though still very fragmentary, certainly suggest that both Equisetales and Sphenophyllales may have sprung from a common stock having certain fern-like characters.

The Equisetales likewise have a long history, and manifestly attained their greatest development in Palaeozoic times.