Never heard of Polk Salad - I'll have to google that one - I love seaweed salad at the Japanese restaurant - that's the best I can do for a strange green - we had beet greens growing up but not collard greens.
I have friends that eat a funky fungus that grows on trees - he calls them sulfers - in my mind I call it YUCK.
I also have a naturalist friend that hunts and gathers wild stuff for the chef's in the Cities and one of them makes a dish using that nasty gross stuff that grows on corn - I call it corn smag - guess it's a case of too each his/her own.
I learned it's not nice to YUCK someone's YUM