This Rhododendron was named for Dr. Royle. Hooker however spelled it Rhodendron roylii. (links to illustration and taxonomic notes)
Rhododendron cinnabarinum var. roylei (Hook. f.) Hutch. is the accepted name.
OBSERVATIONS ON THE VEGETATION AND PRODUCTS OF AFGHANISTAN, KASHMIR AND TIBET.
By J. FORBES ROYLE, M.D., F.R.S., &c.
AUTHOR OF "ILLUSTRATIONS OF HIMALAYAN BOTANY AND FLORA OF CASHMERE,"
" ESSAY ON THE PRODUCTIVE RESOURCES OF INDIA," &C.