Into the woods thenceforth in haste she went,
To seek for herbs, that might him remedy;
For she of herbs had great intendiment,
Taught of the Nymph, which from her infancy
Her nourished had in true Nobility:
There, whether it divine Tobacco were,
Or Panacea, of Polygony,
She found, and brought it to her patient dear
Who all this while lay bleeding out his hart-blood near.
The sovereign weed betwixt two marbles plain
She pounded small, and did in pieces bruise,
And then atween her lily hands twain
Into his wound the juice thereof did scruze [squeeze?]
And round about, as she could well it use,
The flesh therewith she suppled and did steep
To abate all spasm, and soak the swelling bruise,
And after having searched the intuse deep
She with her scarf did bind the wound from cold to keep.
--FQ, Bk III, Canto V, stanzas 32 & 33
--according to the notes in my edition [Penguin Classics, ed. Th. P. Roche Jr, 1987 rpt of 1978 ed], this passage marks the first use in English literature of the word TOBACCO,* the plant having only been introduced to England (by Raleigh) six years earlier, in 1584. I've seen some speculation that athelas might be a relative of tobacco, which makes the parallel all the more interesting, whether Tolkien was deliberately echoing this scene or, perhaps, incorporating an iconic moment well known in myth and epic into his tale.
Hard to say. I know that what once seemed to me a clear borrowing from Spenser on Tolkien's behalf got less so the more you look into it. At first, Spenser's use of TANAQUILL for The Faerie Queene herself's name looks a good candidate as the source for Tolkien's TANIQUETIL for the great mountain of Faery -- except that 'Tanaquil' turns out to be a real person, the most famous Etruscan Queen of Rome, wife of one of the Tarquins. So that Tolkien, being a good classicist, cd just as easily have taken inspiration from antiquity as from Spenser's tale. In any case, a parallel worth noting.
The most important thing of all I'd say Tolkien owes Spenser is his example, of writing a serious, sustained, unapologetic work about Faerie and knights and magicians and dragons and enchantments and warrior-maids and steadfast battles of undaunted heroes against unrepentant evil. Shippey seems to think that Spenser wd be anathama to Tolkien because of the allegory; I suspect Tolkien, like myself and most readers, simply enjoy it for the story, ignoring the allegory as much as possible. Most important of all, Spenser's is the last major English author before Tolkien himself to treat Elves w. respect: his Elf-knights are human-sized but better than humans in strength and courage (it's said in praise of The Red-Cross Knight that although human he's as good as an Elf**). So I'd say he was a significant precursor, but whether an influence is an open question.
*the OED notes several previous uses -- e.g. in Hakluyt's VOYAGES -- wh. presumably the FQ's present-day editor did not count as "literature".
**Red-Cross turns out to be a human raised as an elf, one of the stolen children who are the other side of the changeling tradition.