All parts of pink woodsorrel are edible. But it contains oxalic acid, so keep it in moderation. Not that you wouldn't anyway. The taste is interestingly acrid. Fun to start, but harder to keep going. Many individual immigrants are not problematic by themselves. But in some areas there are just so darn many of them that they become a collective problem. Kind of like the Borg. The trick, if you grow them, is to keep them controlled. Don't let them spread, and don't discard them where they can grow. Here in the North, pink woodsorrel will not be a problem in any case. It won't survive the winter.