Sparkling wax crystals
I'm trying to show those in the first 7 photos.
These are mentioned by George Argus in his Alberta and Flora of N. America descriptions of S. prolixa, they are like minute diamond dust, you need to look with a hand lens or microscope to see them, but they are there!
The white peeling epidermis also seems to go along with the sparkling crystals; he doesn't mention that in the AB or FNA keys, but he does in his CA key at couplet 32 b in the Jepson Manual Online.
http://floranorthamerica.org/Salix_prolixa
https://ucjeps.berkeley.edu/eflora/eflora_keys.php?key=9887