Bog willow is an unusual native species for Massachusetts. The only representative of the mostly northern section Myrtilloides of mostly Arctic subgenus Chamaetia, the most widespread willow of this exotic group, it is a close relative of an Alaskan S. athabascensis and some other species of the Northwest Arctic.
Unfolding first leaves (primordia) are longer than catkin, providing additional layer of protection to flowers.