Isoetes +echtuckerii, hyb. nov., a new triploid quillwort from northeastern North America

A new interspecific Isoetes hybrid, I. echinospora Dur. x I. tuckermanii A. Br., is described from northeastern North America by means of cytology and the scanning electron microscopy of spores. Isoetes xechtuckerii D.F. Brun ton and D.M. Britton, hyb. nov., is the name proposed for this taxon. It is triploid, produces only aborted, sterile spores and has spore ornamentatio n intermediate between that of its putative parents. Populations have been identified in eastern Canada and the adjacent United States of America grow ing in association with one or both parents in shallow, fresh water along o ligotrophic lake and river shores.