Should the d be doubled?
heard as pseuddevernia
spelled pseudevernia
No. pseuddevernia carries one d too many: Pseudevernia.
What the ear did
The d sits exactly on the seam between pseud- and Evernia, and a seam is where doubling looks most plausible in English. Latin joins the two parts with nothing at all, so a single d does the work of both.
P-S-E-U-D-E-V-E-R-N-I-A
The full entry for pseudevernia covers the name itself.