Leaves and stems:

The leafy frond, called a trophophore, is single, 2 or 3 times compound, more or less triangular in outline, 3 to 10 cm (to 4 inches) long, 4 to 12+ cm (to ~5 inches) wide, on a stalk 2 to 8 cm (to ~3 inches) long. The branches (pinnae) each have a few to several segments (pinnules), the largest typically at the base of the branch, the terminal pinnule typically lobed within 1 cm (3/8 inch) of the tip.

At maturity, the largest pinnules are 4 to 9 mm (to ~1/3 inch) long, 2 to 5 mm (less than ¼ inch) wide. The veins are fairly prominent giving the surface a somewhat wrinkled texture. Pinnules are mostly angular in shape and noticeably toothed along the edge.

Spores:

The fertile frond, called a sporophore, is up to 24 cm (9½ inches) long, 1.5 to 2.5 times as long as the tropophore, with numerous branches, each with several to many round capsules of spores (sporangia). Spores are released starting in late September.

Notes:

St. Lawrence Grapefern is native to the Great Lakes region and southeastern Canada and reaches the western edge of its range in Minnesota. Habitats vary, but the preference seems to be moist soil, often in the transition zones between forest and wetlands or grassy clearings, though like many Botrychium species, it may also be found around old mine dumps and tailings basins. According to the DNR, when it was designated as a Threatened species in 1996, fewer than 20 populations were known in the state, but subsequent biological surveys discovered many more so it was not as rare as originally thought and was downgraded to Special Concern in 2013.

Sceptridium (formerly lumped in Botrychium) is characterized by a single compound, generally triangular, evergreen leaf (tropophore) that emerges in spring, persists through winter, and withers away the following summer. The fertile sporophore is not always produced, but when present rises well above the tropophore. S. rugulosum is distingushed by segments (pinnules) mostly angular in shape, the tip edge noticeably toothed, veins fairly prominent so the surface is at least somewhat wrinkled in texture. The largest pinnules are at the base of a branch and are 4 to 9 mm long, 2 to 5 mm wide; the terminal pinnules are typically lobed near the tip. A mature tropophore is 3 to 10 cm (to 4 inches) long, 4 to 12+ cm (to ~5 inches) wide.

Most similar is Sceptridium multifidum, with which it may grow. Both have a few to several pairs of pinnules on each branch, typically the largest at the base and the terminal pinnule lobed within 1 cm of the tip. In most cases it is overall a larger plant, the largest pinnules 9 to 17 mm long and 4 to 8 mm wide, the tips mostly rounded, edges more commonly smooth or scalloped, sometimes obscurely or irregularly toothed, and the veins not prominent so the surface has a flatter texture. When in doubt, the experts say the size of the largest pinnules should be the more important factor.

The difference with the other two species, S. dissectum and S. oneidense, is they have fewer pinnules per branch, the terminal pinnule largest and more elongated, unlobed or lobed more than 1 cm from the tip, the smallest pinnules usually at the base of the branch, and all are distinctly toothed around the edges.