EDIT: Check the comments for some fact-checking. But continue to read behind the cut if you'd like a little "work of poetic imagination."
The ancient Celts followed a lunar calendar, and as such divided the year into thirteen parts. Each of these parts was given a wood, and so when a youngster was born, the child would be made a gift made of their respective fiber.
Since the Celts spanned from Anatolia to Ireland, the different tribes (of course) had to make do with woods native to their region. The following chart is of the Gaels' thirteen natal woods. Because the lunar calendar does not fit into our twelve-month solar calendar, I have chosen to do away with the fixed dates and instead go by how the Gaels did it. I have also given the English name for the trees, with the Gaelic names in parentheses (Scottish in blue, Irish in orange, Manx in red).
If you don't know what moon you were born under, go
here. Remember, it's by the number of new moons after the Winster Solstice (usually December 21), not the Gregorian calendar New Year (January 1). So, like me, you may have to go back to the year before to double check! For example, I was born under the fifth moon cycle of my birthyear, but the sixth after the previous Winter Solstice. Therefore, I'm a hawthorn.
1st new moon phase after Winter Solstice: Birch (beithe, beith, beih)
2nd moon phase: Rowan (caorann/caorunn, caorthann, cuirn)
3rd moon phase: Ash (uinnseann, uinseann, unjin)
4th moon phase: Alder (feàrna, fearn/fearnóg, farney)
5th moon phase: Willow (seileach, saileóg/saileach, shellagh)
6th moon phase: Hawthorn (sgeach, sgeach, drine/drine skeag)
7th moon phase: Oak (darach/darag, dair/darach, darrag/darragh)
8th moon phase: Holly (cuilion, cuilion/cuileann, cullyn)
9th moon phase: Hazel (calltuinn, calltuinn/coll, coull)
10th moon phase: Vine (féith, féith/fíniúin, feeyney)
11th moon phase: Ivy (eidhean, eidheann/eidhneán ini, hibbin)
12th moon phase: Reed (cuiseag, giolcach, guilagh)
13th moon phase: Elder (druman/troman, trom/tromán, tramman)
Interestingly, while I was doing research for this post, I stumbled upon J. K. Rowling's explanation that the wands for Harry Potter, Hermione Granger and Ron Weasley are made of the woods from their Gaelic assignment. They are the only characters whose wands were created using the above calendar. Two trivia for the price of one!