Perennial fern ally 5 - 20 cm tall Leaves: tufted, spirally arranged at top of rootstock, pale toward base, dull green to gray-green or yellow-green, flexible, grasslike, 5 - 20 cm long, linear, slightly swollen near base, tapering to tips. The leaves shrivel, turn yellow and disappear by July, after the spores have matured. Rootstock: underground, bulb-like, two-lobed, brown, nearly round, corky, with roots arising from central area between lobes.
Similar species: Isoetes butleri is quite similar to I. melanopoda, but that species does not occur in calcareous habitats, and the large spores (megaspores) are usually less than 450 microns in diameter, further the megaspores are rarely bumpy but instead obscurely wrinkled with low ridges, and the microspores are gray and spiny.
Habitat and ecology: Incredibly rare, only found in dolomite prairies.
Occurence in the Chicago region: native
Notes: The populations of this species in the Chicago Region are far-separated (disjunct) from the major range of the species, which is in the states of Alabama, Arkansas, Georgia, Kansas, Kentucky, Missouri, Oklahoma, and Tennessee. Apparently this species can be quite abundant in localized habitats of open areas with alkaline soils that are also saturated by early spring rains.
Etymology: Isoetes is from the Greek isos, meaning ever and etas, meanining green, referring to the evergreen character of the plant. Butleri is named after George Dexter Butler (1850 - 1910).
Often ±dioecious (unique among our spp.); lvs 6-20 cm נ0.3-0.7 mm, erect, twisted, whitish or pale reddish-brown toward the base, with abundant stomates and 4 or more peripheral strands; sporangia oblong, 6-10(-14) mm, to one-half covered by the velum, marked with fine brown lines at maturity; megaspores (0.4-)0.5-0.65 mm wide, low-tuberculate or nearly smooth; 2n=22. Terrestrial on thin, seasonally wet soil, mostly over limestone; sc. Ky. to nw. Ga., w. to Ark. and e. Kans.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.