Isoetes x carltaylorii (Isoetes acadiensis x Isoetes engelmannii), a new interspecific quillwort hybrid from the Chesapeake Bay

Isoetes acadiensis Kott is a plant of the Maritime provinces of Canada and the northeastern United States. In the Chesapeake Bay region, this quillwort has previously ben misidentified as Isoetes riparia Engelm., Isoetes saccharata Engelm., or Isoetes saccharata var. reticulata A.A. Eaton, Isoetes x carltaylorii hyb. nov. is the hybrid between I. acadiensis (2 = 44) and Isoetes engelmannii A. Braun (2n = 22). This is the first report of a hybrid with I. acadiensis. An apparently sterile triploid (2n = 33), this rate plant of freshwater tidal marshes has the predicted range of sizes and megaspore features of a hybrid. This brings to 14 the number of interspecific quillwort hybrids described from North America since 1985.