Big surprise today! I have been so many times in that beach park (especially in the last 2 years), with that particular bench to seat and rest after the walk but have never seen this mushroom growing.
It's my fourth locality to see it on Oahu (20 years and I have seen it only on Oahu)! My palm spread is ~24-25cm. When I "measured" the biggest fruitbody of the first group by my palm there were 4-5cm left out of my palm! I didn't "measure" the size of the biggest mushroom in the second group (same Ficus tree trunk, other side, presumably fruitbodies of the same organism) and it looks even bigger?
Pleurotus abalonus (species of the Oyster Mushrooms, this one you have no chance to get in the stores at least here or anywhere as I know!). Very similar to Pleurotus cystidiosus from North America and few more species from Europe, Africa and Australia/New Zealand. Very weathered already: I'm really sorry for not finding them week ago - I have never tried the taste of this one and my assumption is for ~3 pounds (if not more!) when they where fresh!!!
First 3 photos are from group#1. The last one is single photo of group #2...
