Rusty willow is a tree of West European origin, which can grow as
a shrub upon disturbance. It has been aggressively spreading
in coastal New England and included on the Invasive Plant List in 2015.
For a long time it had been taken for a native willow! Rusty
willow, however, is clearly different from any native willow,
because of its smooth, gray, fluted (wavy) bark. The "waves"
on the bark are formed due to extensive ridges on the wood.