I've wondered at the reference to the 'Ivy Tree' in songs like 'North Country Lament', 'Frog's Song' and 'Holly and the Ivy' because ivy is not a tree. Now I've come across a version of North Country Lament (Freddy Grice, Folk Tales of the North Country, 1944)with this lyric:

Oh the oak and the ash and the bonny rowan tree
Do flourish at home in the North Country

So, can anyone confirm the rowan has also been known as the ivy tree?