An established Nuphar advena (Nymphaeaceae) in Massachusetts, U.S.A.

Nuphar advena (Ait.) Ait. f. (Nymphaeaceae) is common and widespread in waters of the eastern United States south of New England with four recognized subspecies (Padgett 2007). Occurrences in the northeastern United States represent the more widespread, typical subspecies (subsp. advena [Padgett 2007]). In New England, this taxon is of conservation concern as Division 2, Regionally Rare (Brumback and Gerke 2013) and currently state-listed as Special Concern in Connecticut (believed extirpated) and Maine (Connecticut Department of Energy and Environmental Protection 2015; Maine Natural Areas Program 2021). Maine occurrences represent highly disjunct populations for the species (Padgett 2007). As part of an aquatic plant identification course, a collection was submitted which contained an unusual Nuphar specimen for Massachusetts, initially identified as the native N. variegata Dur. The leaf had a rounded petiole and divergent basal lobes— features which do not align with N. variegata. To assess the peculiar population, we visited the collection site the following season. Plants growing in this waterbody were determined to be N. advena based on terete petioles and emersed blades (>60 cm above water surface) with greatly divergent lobes (Figure 1). Also consistent with N. advena, the innermost sepals were green on their adaxial surfaces. These plants, previously not known to exist in Massachusetts, were growing throughout the southern shore of the Blue Hills Reservoir (42.22855, −71.05067) in the Blue Hills Reservation. The newly discovered Massachusetts population is well-established, individuals abundant, and all notably robust in size. At the time of observation, plants were flowering and possessed mature fruits. They exhibited the leaf habit typical of freshwater tidal waters with leaf blades positioned in a vertical orientation, parallel with the erect petioles. How the species reached the reservoir is unknown to us, but the history of the site strongly suggests a deliberate introduction. The Blue Hills Reservoir was initially constructed in the 1950s. From 2007–2010, it was completely reconstructed by the Massachusetts Water Resources Authority as part of a water storage project which eliminated the eastern half of the original reservoir (Massachusetts Water Resources Authority 2009). A review of satellite imagery from 2007–2008 (Google Earth Pro 2022) showed the basin was dry during construction. The area was proposed to be re-vegetated as part of the site-enhancement activities of the project (Massachusetts Water Resources Authority