Rowan
Sorbus aucuparia A member of the rose family (Rosaceae), and also known as "quickbeam", "mountain ash" and "sorb-apple", this hardy tree (along with members of its affiliated subspecies) is widely planted in cities in the US and Europe because of its toughness -- along with the conifers, it can survive at the highest latitudes where trees can grow -- and because of its sturdy resistance to air pollution and other environmental abuse. Its white or pink flowers in the spring and its bright orange-red autumn berries (which often last right through the winter if the birds don't eat them all) make the rowan tree extremely popular as an ornamental. But wizards on Earth have more reasons to appreciate rowan trees than just their aesthetic qualities. The rowan has a long history in bardic tradition as one of the major trees of light, deeply affiliated with the Sun (and by reflection, the Moon) and in resonance with light in general and the basic forces involved with sunlight and moonlight.
Rowan trees are often found in the vicinity of sites used for group wizardries. Whether they have been planted there, or have just found their way there themselves, is often a vexed question, best solved by asking the trees themselves, But they are not always forthcoming about answers, having their own agendas in the world, and the wise wizard won't press the question too hard and risk violating the rowans' sense of privacy.
What is certain is that the rowan species are friendly to the Powers that Be, to humanity in general, and to the Art and the wizards who practice it -- hence one of the tree's Celtic names, fid na nDrauaid or "the wizard's tree". A rowan's mere presence in an area often is sufficient to discourage the inroads of the minor servants of the Lone Power; and its wood, when freely given, can be used to make some of the most powerful wands available in Earthly wizardry, extremely effective against the forces of darkness. (SYWTBAW et seq.)
There are any number of resources on the Web discussing the legendry surrounding the rowan in human mainstream culture. Here are a few of them: