Had some thoughts to share regarding house rabbits who eat toxic plants, from a scientific perspective.
I've been keeping house rabbits for some 30 years, and worked with many different rescue groups. I'm also an herbalist, and took a wide array of agricultural courses at Texas A&M University. Rabbits are herbivores, and closely related to deer. Plants that are toxic to dogs, cats, and humans (carnivores and omnivores) may not be toxic to our herbivore friends, even though many lists show them to be. For example, deer love and eat geraniums with no side effects. I had a 6 pound bunny (Snowball) who absolutely loved geraniums...had been eating random bottom leaves off a potted geranium for the 11 years I had her. She never took ill, and never ate more than two or three leaves at a time. She died at 12 years old when her body just wore out.
That said, keep in mind that too much of anything can be bad for your bunnies. There are staple greens that are actually beneficial to their digestion, and then there are greens that neither hurt them nor help them. There are toxic plants to rabbits, but keep in mind that some buns will nibble only enough to get a taste, because they are curious, and won't eat enough to do harm - that would be my NinjaBunny - who one day decided to leap onto the dining room table and eat some Poinsettia leaves, then proceeded to the side table and ate the philodendron. She's a 12 lb Flemmish Giant mix, toughest bunny I've ever met. Luckily, we saw no ill side effects from her taste-tests, and she never thought to eat any again. Just wanted to try them!
Herbivores have something called "biotransformation enzymes" which actually help them to digest plants that omnivores and carnivores find toxic. There are a handful of omnivores that have these enzymes as well (like opossum). Not all rabbits have the same kinds of enzymes, which are inherited. So what could be toxic to one rabbit, may not be toxic to another. Since most rabbits define the term "melting pot" and have a vast pool of DNA from many different species, it is hard to know which bunnies can eat which plants. It is unknown if the biotransformation enzymes are dominant - research is fairly new in this area. If you have a mix, and not a pure bred, chances are your rabbit can eat many plants that appear dangerous, and not get affected.
It is always better to be safe, than sorry, so it's never a bad idea to restrict exposure to toxic plants. Just know that observation is best in these situations, instead of stressing out the rabbit with an emergency trip to the vet, who may or may not fully understand rabbit genetics, and give them unnecessary medications, etc. This information is from Utah State University Agricultural Extension: "Many people assume all plants that contain toxins cause death or decrease production by impairing an animal's physiology. In reality, few toxic plants eaten by herbivores cause overt signs of poisoning. Rather, toxins cause herbivores to limit their intake of plants. At high concentrations, most toxins cause plants to be unpalatable."
http://extension.usu.edu/files/factsheets/Ingestion_of_toxic_plants.pdf