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Pycnoporus cinnabarinus
Small (~11x16mm) orange fungus attached to pruned koa (Acacia koa) branch.
Suburban area on tropical upland plateau.
Spotted on ground intermixed with leaf litter. The four photos are, in order, dorsal (top) view; ventral view; dorsal close-up; and ventral close-up.
Thanks Gully
Although "Mushrooms of Hawaii" by Don E. Hemmes and Dennis E. Desjardin cites sizes of 50-100mm for Pycnoporus cinnabarinus and limits its range (1991 data) to the Big Island (Hawaii--this specimen was seen on Oahu), I think you have it right, and I've edited my spotting to conform.
As a matter of interest, I had a second suggestion, outside this forum, of Laetiporus sp., but that seemed "off."