Amer. Fern. J. 82: 23. 1992.
Plants aquatic, emergent. Rootstock nearly globose, 2-lobed. Leaves deciduous, bright green, pale toward base, spirally arranged, to 45 cm, pliant gradually tapering toward tip. Velum covering less than 1/2 sporangium. Sporangium wall ± brown-streaked. Megaspores white, 460–610 μm diam., cristate to reticulate with thin ridges; girdle obscure. Microspores light gray in mass, 35–30 μm, papillose. 2n = 66.
Phenology: Spores mature in late summer.
Habitat: Flowering water in low woods
Isoëtes boomii is known only from low, wet woods in Laurens County, Georgia. Early collections bearing only microspores were identified as I. flaccida. These were reported as I. flaccida x piedmontana and as having a velum coverage of 70–90% (B. M. Boom 1982), but recent collections have a velum coverage of less than 50%. The megaspore texture of broken lamellae and a narrow velum coverage do not indicate an I. flaccida influence.
Of conservation concern.