QUOTE(CosmicInferno @ Apr 12 2009, 07:22 PM)
i'm not sure but some of the confusion may come from the sources mixing up the common names of the trees. Rowan is Sorbus aucuparia, also known more commonly these days as Mountain Ash. however it is not a 'true' Ash as Ash usually refers to the genus Fraxinus.
i would guess that both are meant to be on the list as they are not interchangeable species, but have similar common names which may have been enough for some authors to mistakenly omit one, which can then be repeated by other sources (particularly online)
That does make a lot of sense. Esoterica: Although I don't know enough about it to say for sure, I've read a lot of articles and researched books that say the tree calendar was never actually based on any historical sources, but as I said I can't say for sure. A bit cautious is all.
The nine sacred woods were unrelated, however. They were supposed to be the woods used to make the sacred fires, who's magical properties worked particularly well together. I think I read something about them being a very strong protective tool when used together, but I can't remember precisely.