Just googled "Turkey Rhubarb" and lo:

http://www.informatik.uni-hamburg.de/~zierke/steeleye.span/songs/turkeyrhubarb.html

Turkey Rhubarb
[Trad. arr. Tim Hart & Maddy Prior]

Tim Hart and Maddy Prior recorded this song for their second duo album Folk Songs of Old England Vol. 2. The record's sleeve notes comment:

Another Bedfordshire song from the collection of Fred Hamer this one being from the singing of Harry Scott. Fred describes this as a "cross between a signature tune and a street call used by a hawker who carried rhubarb in season as part of his stock-in-trade". Although rhubarb in fact came from the mountains between Turkey and Siberia, in the last century anything with a vaguely Eastern origin was attributed to Turkey.

Turkey Rhubarb, Turkey Rhubarb, Turkey Rhubarb I sell
I come here from Turkey to make you all well
Don't you all know me, oh me name it is Dan
For I am the celebrated Turkey Rhubarb man