Hi
I'm not sure if this will help but I use this as a guide. I'v cut & paste from the Brittish Rabit Council Website.
EDIBLE PLANTS
Plants can be either commercially available or wild. Green leafy plants are recommended. Commercially available examples are broccoli, cabbage, chicory, chard, parsley, watercress, celery leaves, endive, raddichio, bok choy, dock, basil, kale, carrot and beet tops. Wild plants include bramble, dandelion, chickweed, plantain, sunflower, wild strawberry, dock, yarrow. Green plants are a useful to provide variety, micronutrients, water and dental wear, but it should be remembered that as they are generally 90-95% water and often relatively low in fibre excessively large amounts would need to be consumed to fulfil daily needs. Therefore they should not be fed in very large quantities. Any greens should be introduced gradually and preferably fed consistently in order for caecal bacteria to adapt.
I've fed our rabbit Chard once when we got it from a neighbour and he loved it. I would only suggest that you give them a small amount maybe to start with.
Please note that I am no expert but I do love my Rabbit :O)
Good Luck