April 15,   Arnold Arboretum, Jamaica Plain, Boston
The invasive European buttercup (known as pilewort) reigning the Arboretum's Meadow early in spring. The Meadow is actually an open wetland, which once used to harbor a vast variety of native plants. Pilewort has been on the rise in such wet open habitats, and especially along brooks. It now presents a problem on the Arboretum grounds.