During 2008 and 2010, we conducted a floristic inventory of the aquatic vascular plants of Yellowstone National Park (YNP). Here, we report noteworthy records found during a survey of over 224 collecting locations within YNP. We documented 26 noteworthy species from 151 collections. These records represent rare, under-collected or newly located species in YNP, Montana, and Wyoming. New records include members of the Araceae (incl. Lemnaceae), Haloragaceae, Hydrocharitaceae, Isoe¨taceae, Lentibulariaceae, Potamogetonaceae, and Typhaceae (incl. Sparganiaceae). During our fieldwork, we located two species new to Montana (Myriophyllum quitense and Potamogeton strictifolius) and three species new to Wyoming (Isoe¨tes echinospora, Najas flexilis, and Utricularia ochroleuca). We also found a single location for P. obtusifolius, a species known historically from Wyoming. In addition, we located P. zosteriformis, a species that had not been collected recently in Wyoming. We also found several species that were either new to the flora of YNP (Callitriche heterophylla, N. flexilis, Potamogeton obtusifolius, P. zosteriformis) or species previously collected in YNP, but were misidentified in herbarium records (Lemna gibba, P. strictifolius, Stuckenia vaginata, and U. ochroleuca). Our work also has greatly augmented the known collections of additional rare species in the Greater Yellowstone Ecosystem such as Lemna valdiviana, M. verticillatum, P. amplifolius, P. friesii, P. robbinsii, and U. minor. In addition, we found new sites for infrequently encountered or easily overlooked aquatic species including Ceratophyllum demersum (Ceratophyllaceae), Elatine rubella (Elatinaceae), Elodea nuttallii (Hydrocharitaceae), Ruppia cirrhosa (Ruppiaceae), and Subularia aquatica (Brassicaceae).