Leaves and stems:

Leaves are basal and palmately compound in groups of 4, resembling a four-leaf clover. Leaflets are 1/5 to 2/3 inch long with smooth or softly hairy surfaces and smooth edges. Stems are sparsely hairy and 1 to 8 inches long. Leaves of submersed plants typically float on the surface of the water while land-locked plants are more erect. Colonies are formed from long rhizomes, rooting at the nodes.

Spores:

Spores are contained in a flattened, round to oval capsule that is up to 1/3 inch long, on a stalk up to 1 inch long. The capsule is initially covered in hairs but quickly becomes smooth. The spore stalk arises from the rhizome at the base of a leaf stalk.

Notes:

Although this fern may not bring you luck as a four-leaf clover might, you could count yourself lucky if you happen to see it within the state, as it is currently endangered in MN. While in other regions it can be found in pond edges, floodplains, and other low areas with fluctuating water levels, in MN it is limited to ephemeral pools in rock outcrops and shallow prairie pools. According to the DNR, it was listed as an Endangered species in 1996 due to its few numbers and very specialized habitat, which is at risk of destruction from mining and over-grazing, plus excessive herbicide use for weed control in pastures. This is only Marsilea species found in Minnesota.