This name is a synonym of Isoetes engelmannii A. Braun.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 26604199) with original publication details: Manual (ed. 5) 677 1867.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:308604-2.
This name was in version 1 of The Plant List, record tro-26604199.