Holly. One of the loveliest of plants through the seasons, it is said to shelter forest sprites in winter - among many other real birds and animals. Holly is a vital food source for birds but it is toxic to humans and animals. Holly leaves have been made into a tea to treat measles, pneumonia, colds and flu, although we can't vouch for that. Individual trees are either male or female, so they like to be near each other to produce berries. We source the best holly trees in the UK.