Lorien

[Sophia the Thunder Mistress]

I've never heard of the book mentionng them except in Numenor which only one Mallorn grew.

I believe that the Mellyrn (the Sindarin plural of Mallorn) were brought to Númenor from Tol Eressëa and they grew thickly in the region of Nisimildar in southwest Númenor and less frequently elsewhere on the island. Gil-galad did give Galadriel her first Mellyrn, but these were brought to him from Númenor by Tar-Aldarion.

One other Mallorn grew outside Lórien which hasn't yet been mentioned: the one that grew from Sam's seed in the Shire.