Q. ‽farnë (farni-) n. “ash, rowan”
A Quenya noun for the rowan-tree, appearing in an explanation of the name Orofarnë “Mountain Ash” in notes from the 1950s, though Tolkien marked it with a “?” as uncertain (PE17/83). Its older form was either fărnĭ or primitive ✶pharne; if the former, its stem form would be farni-.
Conceptual Development: In the Etymologies from the 1930s, a similar word ᴹQ. ferne appears as the Quenya word for “beech-tree” (Ety/PHER). Conversely, ᴹQ. farne appeared with the gloss “foliage” as a derivative of ᴹ√PHAS (EtyAC/PHARAN, PHAS). Since the beech and the rowan are similar species of trees, it is possible that Tolkien intended to replace ferne < ᴹ√PHER(EN) with farnë < √PHAR(AN).
Neo-Quenya: For the purpose of Neo-Quenya writing, I think you would be better off using the earlier but better-known word ᴹQ. ferne for beech-trees and their relatives, to avoid conflicts with derivatives of the root ᴹ√PHAR “suffice”. For the sense “foliage”, it might be better to use the later word olass(i)ë.
References ✧ PE17/83