Butomus umbellatus Established in Massachusetts

Butomus umbellatus L. (Butomaceae), flowering rush, is an emergent, perennial, wetland species of lake margins or slow-moving waterways. Native to Europe and western Asia, its initial North American introduction—most likely as a water garden escape—was reported from the St. Lawrence River (1897), and by 1929 it was established in Lake Champlain, Vermont (Les and Mehrhoff 1999). Based on herbarium records, plants were subsequently discovered in Connecticut (1943) and Maine (1999), where stations are currently known from a few counties, respectively. In New England, it remains most abundant and invasive in Vermont. During a 2006 floristic inventory related to a weed management project, Butomus was first observed in Massachusetts flowering on the western shore of the eastern basin of Winter Pond, Middlesex Co., Winchester (GeoSyntec 2006). Sterile specimens were later vouchered in 2008 from the north shore of the same basin and serve as the first collection (Mehrhoff 23282; CONN). After a few unrelated pond assessments (2016, 2017) failed to note individuals, a July 2019 shoreline survey documented the species’ successful establishment around most of the eastern basin’s (‘‘Little Winter Pond’’) periphery, where plants were flowering at multiple locations. The Butomus umbellatus colonization of Winter Pond is noteworthy, not only as the first Massachusetts occurrence of this alien, but seemingly as its first establishment within the Atlantic coastal plain pond ecosystem of New England. Winter Pond, divided into two basins, is a 17 acre kettle hole depression that experiences natural, seasonal water drawdown. The periodically exposed, sandy shorelines of these ecosystems support a unique floral community often including sensitive, globally restricted species (Sorrie 1994). Winter Pond, and its remarkable flora, has been well acknowledged in the literature (e.g.,