All parts of the Elder plant is toxic, including the berries that are so frequently used in foods and certain wine production. The only way to consume the berries of elders safely is to cook the MATURE berry. There are some sources that believe as long as the berry is fully ripe, that it is harmless.
Every other part of the elder plant, though, is highly toxic--the leaves, branches, bark and especially the roots--containing a glycoside that produces cyanide when it has been metabolized by the body's digestive system. So, medicinal teas made with elder leaves should be consumed with caution. The wines and marmalade made from mature berries are perfectly safe.
The power of the poisonous Elder tree has been revered since ancient times, where the presence of an Elder tree was meant to ward off evil and protect the area from witches.. though, conversely, several folk tales have witches congregating beneath the Elder trees, especially when they were ripe with fruit.
There is also the belief, in some regions, that to cut down an Elder tree is to ask to be cursed by the Elder Mother, a tree spirit that would be released to take revenge. The only way, it is said, to be safe from the curse of the Elder Mother is to first ask her permission to cut down the tree. Variations of the following chant were used to protect the woodsmen from the spirit's revenge:
Old girl, give me some of thy wood and I will give thee some of mine when I grow into a tree.
Guard me, elder mother, let not the wood-ax fall,
protect with your mighty strength my tender fruits, my wistful leaves.
Guard us, let not the woodland foe destroy us all,
As nothing, for all mankind, in this world, his greed will appease.
Fear not! Hear my promise, oh, gentle, forest child,
think nothing of the heartless woodsmen as they stomp and curse and burn.
They will be the ones to tremble in the wild,
when the forgotten might of nature, at last, and all at once returns.
--- e.a.s demers