| Horsetail | perennial rushlike flowerless herbs with jointed hollow stems and narrow toothlike leaves that spread by creeping rhizomes |
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| Horsetail | sole surviving family of the Equisetales: fern allies |
| Horsetail | any of several lichens of the genus Alectoria having a thallus consisting of filaments resembling hair |
| Horsetail | milkweed of southwestern United States and Mexico |