Ann. Missouri Bot. Gard. 9: 135. 1922.
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.
Phenology: Spores mature in winter or spring.
Habitat: Shallow depressions on granite outcrops
Isoëtes lithophila is known from granite outcrops in Burnett, Mason, and Llano counties in south central Texas.
Of conservation concern.