Firstly, what kind of tree are the Two Trees? I think considering Galathilion is referred to as a “silver cherry” and it’s a seedling of Telperion this suggest the Two Trees were in fact bioluminescent, ever-flowering cherry blossoms with silver and golden bark and flowers. The mallorns are also described as being cherry-like and the seed Galadriel gave to Sam is described as being much like an un-shelled almond.
Of the Silmarils it was said “Like the crystal of diamonds it appeared, and yet was more strong than adamant…the house of its inner fire of the Silmarils Fëanor made of the blended light of the Trees of Valinor."
I think we are looking at some kind of fortified diamond. Much like mithril is “true silver”. Maybe Feanor discovered carbon fibers?
So yeah, I think it’s cherry blossoms and diamonds.
Mallorns are described in a couple of places as being birch-like, but to my mind they resemble beeches more closely. Tall trees with sliver-grey bark sound like beeches to me. Note as well that a beech hedge will often retain its dead, yellow leaves all winter, like a mallorn. Beeches give nuts, too.
But the Two Trees and their scions, and mallorns themselves, are all definitely flowering trees, so they resemble cherries in this respect much more than birches or beeches.
What’s to say that they were the same species as any modern tree? The weight of the evidence would seem to be that they’re not: After all, no modern tree glows.
There used to be a BIG old Magnolia tree in the Mission Valley Shopping Center in San Diego, and this was always my “Mallorn” tree. The leaves were green on top, and gold underneath, and it had big luscious white blossoms in the Spring. The bark was somewhat silvery grey. It was easily big enough to build a tree-fort (Tolkien’s flets.)
Tolkien himself designed a cover picture for The Return of the King, which incorporated the White Tree and Seven Stars, and the crown and throne of Gondor:
[He had a surprisingly modern design for the throne.]
The blossoms are sort of cherry-like. I was under the impression that cherry trees usually had a tall trunk with a ball of foliage at the top. Tolkien seems to have envisioned it with branches all the way to ground level, like a pine or a spuce.
They lose their leaves in winter, and they’re quite flimsy, as trees go; I don’t think I’ve seen any suitable for a flet.
I envisage them as something similar to a kauri tree, except the leaves are a bit wrong. And they don’t flower. And I doubt Tolkien was familiar with them. They’re seriously spectacular trees though.
My daughter studies genetic engineering, and adding a fluorescent gene is commonplace. Note that you need a source of blacklight (UV) to make it glow. Tolkien doesn’t mention that.
They were gigantic magical fantasy trees. Made by gods. Their essence was used to create the sun an the moon. There was only one of each and they existed in a time that was mythological to a world that is fantasy.
They were not cherries, oaks, coconut palms or any other ‘mortal’ tree.