From my vet, generally greens that are safe for humans and horses are safe for buns. Same with herbs. There are a few like spinach and parsley that should be eaten in moderation. Kale and other brassicas are controversial, Dorian loves it and has no issues… so best bet there is start simple and then slowly add one by one and monitor. Rabbit digestion isn’t like human digestion, so just cause they give humans gas doesn’t mean your rabbit will get gas. That’s said some buns don’t do well with them, which is why introduce one at a time. Romaine is great starter. House Rabbit society has a great list of green. I did find the allowed not allowed gets pretty damn confusing (different site would wildly contradict each other, even ones that were both reputable) so I seriously quizzed my vet when I first got Dorian. I also read any study I could find, and tried to go through some of the veterinary literature. It’s been a bit, but if you want I can go dig and see if I can find some links. Good diet is important after all!
Side notes: the oxalic acid in kale varies between varieties, some are actually pretty low. Moderation is however a good idea, especially since figuring out which variety has what amount is challenging.
domestic and wild buns (especially if you are referring to contain tails commonly found in N. America) have different digestions, what can be eaten by one can seriously upset the tum of the other… so just because a wild rabbits chomping down and seems unharmed, doesn’t mean it’s a good food for your bun. I hadn’t realized that until I read up on it, so thought I’d mention 🙂