Leaves and stems:

The sterile stem is green and has whorled branches that are spreading to ascending. The “leaves” are reduced to a sheath that surrounds the stem with 4 to 14 black/brown teeth at the top, often with 2 or 3 teeth joined along an edge. The stem has a small central cavity; branches are solid (not hollow) and 3 or 4 angled. The first sheath on the branch (aka first internode) has 3 or 4 teeth. The first branch internode is distinctly longer than the stem sheath.

Fruit:

Fertile stems are not like the sterile stems, identified by the ½ to ½-inch, blunt-tipped cone at the tip of the stem, stout flesh-colored stem, and lack of branches. The teeth on the stem sheath are much larger than on the sterile stem. Fertile stems are seen only in early spring and whither away after releasing the spores. Spores are white.

Notes:

Field Horsetail is something of a weedy species, often found along grassy roadsides and paths, spreading both by spores and vegetatively through rhizomes, and may create large colonies. It may be confused with Marsh Horsetail (Equisetum palustre), which has 5 or 6 teeth on the branch sheath and its first branch internode is shorter than the stem sheath. Also similar is Meadow Horsetail (Equisetum pratense), which, like E. arvense, has 3 or 4 teeth on the branch sheath, but its first internode on the lowest branch is shorter than the stem sheath and branches are spreading to drooping (not ascending). Note that it is important to look at the lowest branch when trying to determine if the first internode is longer or shorter than the stem sheath. On E. pratense; the first internode on branches further up the stem may be as long as or very slightly longer than the stem sheath. Field Horsetail is not very picky about habitat and may be found in shady woods or sunny open areas, frequently in disturbed soils. The sterile stem growth habit varies accordingly, with long, spreading branches (more similar to E. pratense) in moister, shadier locales and growing prostrate or almost shrub-like with multiple stems from the base in sunnier, drier soil.