I had the same problem in beta and I forget how I fixed it. For some reason they weren't showing up on my screen due to a graphics problem. Try adjusting your graphics until you can see them and make sure you have someone in the zone show you where they see them so you can be sure it's not just you looking in the wrong places.
They are near Crushbone Brute's behind the tents in around the rocks.
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__________________ Fly High Daevas, Tamat ~ Andrew Beegle Community Manager
I have this quest with an alt and could not find the mushrooms either. Changed settings to Balanced... now i can see mushrooms everywhere but they are not harvestable...
hmmm what the heck. That used to be a problem in beta but they fixed it. Guess it's happening again though. Please make sure to do a bug report and maybe even a petition about what's happening to you.
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__________________ Fly High Daevas, Tamat ~ Andrew Beegle Community Manager