The herb is “tobacco” (through Spanish probably originally from Carib) – in The Hobbit and “pipe-weed” (spelled as one word without hyphen and formed in English out of English parts) in later works.  In his Letters, Tolkien refers to the tobacco essay in his Appendices.  I know that our fellow scholars have addressed the substitution of the latter word for the former.  I’m counting on you, Word Fans, to point out articles on these words in our Comments section.  Tolkien mentions tobacco and pipe-weed in the same sentence in a 1958 letter to Rayner Unwin.

In this home of ‘smoking’, pipe-weed seems specially to have caught on. There were clay pipes on the table and large jars of tobacco –

We have elsewhere the uncommon word “tobacco-jar“.  Now, may I present “tobacco”?

• 01.010 And a very fine morning for a pipe of tobacco out of doors,
• 02.027 and tobacco.
• 05.004 and there was some tobacco
• 05.004 and the smell of tobacco

“pipeweed, n.” OED Online. Oxford University Press, March 2016. Web. 10 March 2016.

“tobacco, n.” OED Online. Oxford University Press, March 2016. Web. 10 March 2016.

Tolkien, J.R.R. (2014-02-21). The Letters of J.R.R. Tolkien (Kindle Locations 5661-5662). Houghton Mifflin Harcourt. Kindle Edition.