Boom's quillwort

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.

Spores mature in late summer. Flowering water in low woods; of conservation concern; Ga.

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.