Leaves and stems:

The leafy frond, called a trophophore, is single near the base of the stem, oblong to egg-shaped in outline, usually with 1 to 5 pairs of leaflets (pinnae); occasionally only a terminal pinna develops. The trophophore is 1 to 5 cm (to 2 inches) long, held erect to ascending, its stalk 0 to 2 cm (to ~¾ inch) long. The stem below the tropophore is 1 to 3 cm (3/8 to ~1 inch) long.

Pinnae are ascending, irregularly shaped, spoon to wedge-shaped to squarish, and span an angle of 30 to 90 degrees. The lowest pair is typically more strongly ascending than those above it and is largest, sometimes significantly so, appearing to be 3 separate leaves coming from the base of the stalk. The tip edge is usually smooth, sometimes scalloped, occasionally shallowly notched.

Spores:

At the top of the stem is the fertile frond, called a sporophore, 3 to 14 cm (to 5½ inches) long, typically rising well above the tropophore, the stalk portion 3 to 8 cm (to 3+ inches) long, up to 4 times as long as the tropophore. The sporophore typically has several short branches, each with a few to several round capsules of spores (sporangia) that mature starting in early July.

Notes:

Least Moonwort is one of the more common Botrychium species in Minnesota, found in a variety of habitats including forests, prairies, swamps, old fields and homesteads, and abandoned mine dumps and tailings basins, more often in open sites than in shade. According to the DNR, B. simplex was listed as a Special Concern species in 1996. At the time there were 3 varieties thought to be in Minnesota: var. simplex, the most common (and as described above); var. compositum, now considered stricly a western species with large, divided basal pinnae and found primarily in seasonally dry meadows; and var. tenebrosum, now split to separate species B. tenebrosum (Swamp Moonwort).

Botrychium simplex is distinguished most easily by the length of the stem below the tropophore: typically very short so the tropophore splits off near ground level. The sporophore stalk also tends to be quite long, up to 4 times as long as the tropophore. Pinnae can be really variable, both in number and shape; a robust plant often has a basal pinnae pair nearly as large as the rest of the tropophore, where a weak, demure plant may have just a terminal pinna, without lateral pairs.

It is no surprise that B. tenebrosum is most similar and distinguishing the two is not always easy, but a reasonably consistent difference is the tropophore splits off the stem about half the length of the plant, though where this split occurs is not always the same for either species.

Keep in mind that Botrychium identification can be difficult even for the experts so don't be discouraged if you struggle to get it down to species.