I agree that the seriousness of a canine eating a poisonous plant will depend on the particular plant, the size of the dog and the amount of the plant that's ingested.
45 years ago I worked with someone who raised Saint Bernards and one year, one of their dogs ate part of a Poinsettia plant (Euphorbia pulcherrima). They rushed the dog to the Veterinary Clinic because he was quite sick but luckily he survived. The veterinarian told them that if it had been a much smaller breed dog and depending on the quantity of the plant ingested, it could have be fatal.
We have 3 dogs and two of them are Golden Retrievers who always want to eat leaves, wood mulch, sticks, etc., so much so that I've always referred to the two of them as our "Goat Dogs." We live in Florida, with many tropical plants that are poisonous to dogs. I browse our backyard on a regular basis and I've pulled up numerous Solanum diphyllum seedlings, Epipremnum aureum (Pothos) vines and Lantana seedlings among other plants. Our dogs are never outside unsupervised but even with supervision, it's sometimes hard to keep track of all three of them.
