0xd7 in species name ?

[Robert A. (Bob) Morris]

USDAPlants uses the "times sign" 0xd7 for many Quercus (and other)
species, e.g. Quercus X acutidens (which can be found with a search
Quercus acutidens ). Here I render "X" as does ITIS.  IPNI omits it altogether

Can someone tell me:

a. What is the meaning of the "X"

b. Aren't taxon names required by ICBN to be entirely in Latin
characters? If yes or no, can someone provide references to ICBN
article and perhaps to Winston's book (Judith Winston, "Describing
Species"). In Winston, I see such a claim for ICZN but not that I can
find for ICBN.

c. Does ICBN support IPNI, ITIS, or both as accepted names.

Thanks
Bob, Not a Biologist, Morris