The version of "American Stranger" I sing has the verse thusly:

"The ships upon the salt salt see may sail without a sail
The little wee fishes grow 'till they turn into muckle whales
In the middle of the ocean will grow a rowan tree
If ever I prove false to her that's given her love to me."

Ewan MacColl has said that versions of "The Plains of Amerikee" date back to before the American Revolution, but since we're deeling with such a formulaic verse, it could have been inserted at any time.

I suspect we may only find the true answer when apples grow on an orange tree....

Dan Schatz