Leaves and stems:

Sterile frond is a single, undivided leaf, lance-elliptic to egg-shaped, 2 to 4 inches long and up to 1½ inches wide, widest in about the middle, blunt or rounded at the tip, gradually tapering at the base, and sheathing the short stem. The leaf blade is hairless and erect to spreading. The sheath is membranous and soon disintegrates.

Spores:

The spike-like fertile frond emerges from the leaf sheath, the stalk eventually elongating up to about 5½ inches, with 2 opposite rows of spore producing structures at the tip. The spike is ¾ to 1¾ inches long. Spores turn brown when mature.

Notes:

It doesn't look much like a fern. While this is the only species in the Ophioglossum genus present in Minnesota, there are about a dozen species in North America. One of the interesting distinguishing characteristics is the venation on the leaves. They are typically covered in a network of distinct, roughly circular veins called “areoles”. The pattern of areoles as well as the vein pattern inside an areole can be diagnostic. In the case of O. pusillum, the veins inside the areoles are free, i.e. not all connected to the edge of the areole. The next closest Ophioglossum species to Minnesota is Southern Adder's-tongue (O. vulgatum), which is found as far north as the southern edge of Wisconsin. In some references O. pusillum is listed as a variety of O. vulgatum but has since been separated. O. vulgatum is most easily distingushed by its persistent, leathery leaf sheath and damp forest habitat.