I am reading The Return of the King, and when I got to the chapters concerning the Battle of the Pelennor Fields, something struck me. Earlier in the story, Theoden was shocked to see Merry and Pippin smoking "pipe-weed", which was almost unknown outside of the Shire; intrigued, he promises Merry that they will go to Edoras and Merry can tell him about this strange habit.
In RotK, as Theoden lays dying, he tells Merry that he regrets that he will not be able to fulfill his promise.
"Pipe-weed", of course, is tobacco. And therein lies the problem. Since Middle-Earth is stated by Tolkien to be in a pseudo-historical, pre-historic Europe, how did non-European plants like tobacco get there before the 'modern' age? Does Tolkien provide any explanation?
Then I remembered additional examples: Bilbo served tomatoes at his party, and Sam wished he had potatoes for his rabbit stew, and then pined for fish and chips ("chips" being French fries, also made from potatoes). These are also not native to Europe.
But of course, no one in The Lord of the Rings seems to know that other continents exist, and I don't know of any reference to an analog of the Americas in Tolkien's legendarium. It seems unlikely that anyone had ever traveled between Middle-earth and the Americas, to say the least.
Doing a little research, I found an entry on tomatoes at Tolkien Gateway, which states that tomatoes were also mentioned in the original version of The Hobbit, but Tolkien later changed the word "tomatoes" to "pickles", presumably because of the issue I am addressing here.
Did Tolkien ever address how these plants came to Middle-earth, or admit that their presence there doesn't make much sense?
Note: Many people have been arguing that Middle-earth is not necessarily supposed to be on our planet earth. From Tolkien's perspective, this argument is nonsense. I will let him address this topic in his own words (all quotes are from Tolkien's letters unless otherwise noted):
‘Middle-earth’, by the way, is not a name of a never-never land without relation to the world we live in (like the Mercury of Eddison). It is just a use of Middle English middel-erde (or erthe), altered from Old English Middangeard: the name for the inhabited lands of Men ‘between the seas'. And though I have not attempted to relate the shape of the mountains and land-masses to what geologists may say or surmise about the nearer past, imaginatively this ‘history’ is supposed to take place in a period of the actual Old World of this planet.
May I say that all this is ‘mythical’, and not any kind of new religion or vision. As far as I know it is merely an imaginative invention, to express, in the only way I can, some of my (dim) apprehensions of the world. All I can say is that, if it were ‘history’, it would be difficult to fit the lands and events (or ‘cultures') into such evidence as we possess, archaeological or geological, concerning the nearer or remoter part of what is now called Europe; though the Shire, for instance, is expressly stated to have been in this region (I p. 12).6 I could have fitted things in with greater versimilitude, if the story had not become too far developed, before the question ever occurred to me. I doubt if there would have been much gain; and I hope the, evidently long but undefined, gap in time between the Fall of Barad-dûr and our Days is sufficient for ‘literary credibility’, even for readers acquainted with what is known or surmised of 'pre-history'.
I have, I suppose, constructed an imaginary time, but kept my feet on my own mother-earth for place. I prefer that to the contemporary mode of seeking remote globes in ‘space’. However curious, they are alien, and not lovable with the love of blood-kin. Middle-earth is (by the way & if such a note is necessary) not my own invention. It is a modernization or alteration (N[ew] E[nglish] D[ictionary] ‘a perversion’) of an old word for the inhabited world of Men, the oikoumenē: middle because thought of vaguely as set amidst the encircling Seas and (in the northern-imagination) between ice of the North and the fire of the South. O.English middan-geard, mediæval E. midden-erd, middle-erd. Many reviewers seem to assume that Middle-earth is another planet!
As for the shape of the world of the Third Age, I am afraid that was devised ‘dramatically’ rather than geologically, or paleontologically. I do sometimes wish that I had made some sort of agreement between the imaginations or theories of the geologists and my map a little more possible.
I imagine the gap [between TA and now] to be about 6000 years: that is we are now at the end of the Fifth Age, if the Ages were of about the same length as S.A. and T.A. But they have, I think, quickened; and I imagine we are actually at the end of the Sixth Age, or in the Seventh.
In (5) we meet the conception of the dragging of Tol Eressëa back eastwards across the Ocean to the geographical position of England - it becomes England (see I.26); that the part which was torn off by Ossë, the Isle of Íverin, is Ireland is explicitly stated in the Qenya dictionary. The promontory of Rôs is perhaps Brittany.
-The History of Eriol or Aelfwine. [This was among the earliest writing Tolkien did regarding Middle-earth, and later, he decided against the idea of "dragging" an island to the current location of the British Isles; instead, he chose to say that the seas eventually rose and surrounded the Shire, turning it into the British Isles]
Were he here today, Tolkien would insist, as he frequently did during his own lifetime, that Middle-earth is absolutely, unquestionably, without any doubt, and with complete certainty, a place in our own world, roughly analogous to a prehistoric version of modern Europe (the LotR wiki has even produced a map showing how Middle-earth and Europe would presumably align). Arda is meant to be earth, albeit in the distant past.