When Mix first described Taphrina populi-salicis in 1947, he listed Salix laevigata as a host. But in 1956 he concluded that the willow-like leaf that led to the "-salicis" part of the name was actually a Populus trichocarpa leaf -- possibly var. hastata--that was long and narrow and looked very much like willow.

See pg 468 of Mix, Notes on Some Species of Taphrina. Transactions of the Kansas Academy of Science (1903-), Vol. 59, No. 4 (Winter, 1956), pp. 465-482
https://www.jstor.org/stable/3626314.

"The specific epithet of the fungus becomes an unfortunate misnomer," he wrote.