Salix serissima (L.H.Bailey) Fernald
Family: Salicaceae
autumn willow
[Salix lucida var. serissima Muhl.]
Salix serissima image
from USDA Plants website  
Etymology: Salix: Latin name for the willow and meaning "to leap or spring" in reference to its fast growth
Plants: perennial tree 3 1/2'- 13' tall
Leaves: lance-like to oblong, shiny dark green above, underside whitened
Flowers: much like S. pentandra but with shorter catkins
Habitat: swamps, bogs
Conservation Status: Native