The genus Isoetes is easy to recognize, but the distinctions
between species are more challenging. Fortunately we have only
two species in Wisconsin, of the 24 species reported for North
America. The most reliable means of identifying the species of
Isoetes requires observation of the megaspores with a microscope.
Megaspores of I. echinospora are covered with numerous
spines, and are easily distinguished from the curving ridges of
I. lacustris megaspores.
I. lacustris grows on lake beds, usually completely submersed
in the water and often overlooked. The water must be reasonably
clear to allow Isoetes to grow on the lake bed and most
known locations are of oligotrophic lakes (i.e. of low productivity)
with slightly acid water.