Rock quillwort

Plants becoming terrestrial. Rootstock nearly globose, 2-lobed. Leaves deciduous, bright green, pale toward base, spirally arranged, to 12(--20) cm, pliant, gradually tapering to tip. Velum covering entire sporangium. Sporangium wall unpigmented. Megaspores light gray to gray-brown, 290--360 μm diam., obscurely rugulate with low ridges; girdle obscure. Microspores brown in mass, 30--33 μm, tuberculate to spinulose. 2n = 22.

Spores mature in winter or spring. Shallow depressions on granite outcrops; of conservation concern; Tex.

Isoëtes lithophila is known from granite outcrops in Burnett, Mason, and Llano counties in south central Texas.