This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Isoetes Butleri Engelm. Coult. Bot. Gaz. 3: 1. 1878.
Terrestrial from a subglobose trunk. Leaves 8-60, bright green, paler at the base, triangular, 3'-7' long, bearing numerous stomata, and with well developed peripheral bast-bundles, thick dissepiments and small air cavities within; sporange usually oblong, spotted; velum very narrow or none; ligule small, triangular; dioecious; macrospores 400-630 μ in diameter, with distinct or confluent tubercles; "microspores 28-34 μ long, dark brown, papillose."
On rocky hillsides, Illinois and Kansas, southward to Tennessee and Oklahoma