Spirodela oligorrhiza (Kurz) Hegelm., a member of the family Lemnaceae, as reported thus far, has a rather irregular distribution in the United States. This species has been reported from Missouri, California, Florida, Louisiana, Illinois (Daubs 1962a) and more recently from North Carolina (Harrison and Beal 1964). This species has not been previously reported to occur in Pennsylvania or the neighboring states of Ohio and West Virginia.