Black-footed quillwort

Plants terrestrial or becoming so. Rootstock nearly globose, 2-lobed. Leaves deciduous, bright green, pale to lustrous black toward base, spirally arranged, to 40 cm, pliant, tapering gradually to tip. Velum covering less than 3/4 sporangium. Sporangium wall brown-streaked. Megaspores white, 280--440 μm diam., obscurely rugulate with low ridges, rarely tuberculate or reticulate; girdle obscure. Microspores gray in mass, 20--30 μm, spinulose. 2n = 22.

Spores mature in late spring. Noncalcareous soil; meadows, fields, ditches, soil pockets on rock outcrops; Ark., Ga., Ill., Ind., Iowa, Kans., Ky., La., Minn., Miss., Mo., Nebr., N.J., N.C., Okla., S.C., S. Dak., Tenn., Tex., Utah, Va.

Population of Isoëtes melanopoda in New Jersey, North Carolina, South Carolina, Utah, and Virginia are disjunct.

Plants of Isoëtes melanopoda with black leaf bases are typical. Plants without black leaf bases have been called I. melanopoda f. pallida (Engelmann) Fernald. Variation also occurs in megaspore morphology. A collection from Dallas County, Texas, has lustrous black leaf bases and boldly rugulate spores with ridges that occasionally anastomose. In many respects, I. melanopoda is similar to I. howellii.