Isoëtes flaccida includes individuals with a variety range of megaspore sizes and textures. Although megaspores are fairly uniform among individuals within a population, considerable variation occurs between populations. A local Florida population with megaspores that are nearly smooth on the proximal faces and low-tuberculate on the distal hemisphere has been described as
I. flaccida var
chapmanii Engelmann.
Isoëtes flaccida var.
alata (Small) N. E. Pfeiffer has included plants in which the megaspores are densely tuberculate to rugulate on the proximal faces and have bold, anastomosing ridges on the distal hemispheres.
Isoëtes flaccida hybridizes with I. engelmannii
