Rush-like green plants with jointed usually hollow stems from running rootstocks; the branches verticillate, with toothed sheaths at the nodes, and when fertile bearing the sporangia beneath the scales of the terminal cone-shaped spikes.
I. Equisetum. (Tourn.) L.
1. E. arvense. L. Field Horsetail.
2. E. pratense. Ehrh. Thicket Horsetail.
3. E. sylvaticum. L. Wood Horsetail.
4. E. scirpoides. Michx. Rush Pipes.
5. E. fluviatile. L. Swamp Horsetail.
6. E. variegatum. Schleich. Variegated Horsetail, 7. E. hyemale. L. Scouring Rush.