Are there any records of words in Sindarin for specific plants? For example, rose, lily, ash, oak??? I'm asking because of personal interests in learning these plant names. The two I'm most interested in finding out about are lily and hawthorn. Please and Thank You!
There are definitely specific plant names in Sindarin! Unfortunately, there is no attested word for “lily” (though a neologism could be crafted if you really would like a Sindarin word for “lily”). “Hawthorn” is tadhos, “rose” is meril, “ash/rowan” is faran, and “oak” is nordh.
For "oak" I would rather recommend using doron, as it is etymologically clearer than nordh, and its Q. cognate norno is also attested in the late period.
As for "lily" - one option for a neologism would be to look at Q. indil/insil. Tolkien had two versions of this word: one (insil), appearing in the 1950s, was loaned from Mannish inzil; the other (indil), likely attested later (1959-1960), derived from Valarin iniðil.
The first of these etymologies requires discarding the Valarin word, and it is also the earlier of the two; for these reasons Paul Strack prefers the second etymology, and suggests that the Mannish word was in turn loaned from (archaic) Quenya †inðil.
Whether that is likely or not is a separate topic. What matters in this instance is that both inzil (from Mannish) and inðil (from archaic Quenya), if loaned into Sindarin, would produce the same result: S. innil.
This is certainly not the only option for producing a neologism for "lily", mind you. There are some early period words that could perhaps be updated to fill this semantic space, and other ideas can be entertained too. This is just one option (and I will not claim it is necessarily a very good option).