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, thi s quillwort has previously been misidentified as Isoetes riparia Engel m., Isoetes saccharata Engelm., or Isoetes saccharata var. reticulata A.A. Eaten. Isoetes xcarltaylorii hyb.nov. is the hybrid between I. ac adiensis (2n = 44) and Isoetes engelmannii A. Braun (2n = 22). This is the first report of a hybrid with I. acadiensis. An apparently steril e triploid (2n = 33), this rare 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 f rom North America since 1985.