Again the question regarding what plants had made it to Western Europe prior to the 1600's - this time I'm Looking at Brassica napus.
While Tomatoes may or may not be something seen in pre-1600s Western Europe, Brassica napus specifically the Rutabagas/Swedes varieties only show up later.
Brassica rapa (turnip) vs Brassica napus (canola, rapeseed, and rutabaga) cultivation and where and when.
Turnips are a staple of the Western European diet prior to the 1600's however rutabagas were not. The first text reports of rutabaga are from 1620 by Gaspard Bauhin in Switzerland - however it may have been was introduced from Russia.
So I wondered if there was any evidence of rutabaga used earlier in Russia. Seeing as it wouldn't necessarily be called rutabaga, and the genus -species is sort of imprecise in terms of what the brassica looks like (canola, rape seed, and rutabaga are fairly different in how they look currently). The idea is that rutabaga was at some point a spontaneous cross between rapa and napus....I had to look up the genetics of that but the gist is that it is likely to occur spontaneously if the crops are grown in close proximity.
Then I found
Russian Journal of Ecology, Vol. 33, No. 6, 2002, pp. 388–391. Translated from Ekologiya, No. 6, 2002, pp. 412–415.
Original Russian Text Copyright © 2002 by V. Tuganaev, A. Tuganaev.
Medieval Agroecosystems (9th–13th Centuries) in the Region of the Present-Day City of Glazov (Udmurt Republic)
V. V. Tuganaev and A. V. Tuganaev
Which basically shows, aside from a fair number of other crops, they had both napus and rapa found at the same cultivated site. What variety the napus is (rape seed or rutabaga) is unclear, but the rapa variety is turnip. So it makes me wonder if perhaps this site was where the coss occurred. They class both Turnip and Rutabaga as being cultivated at the site in the conclusion. Other crops at the site (and the reason I have the paper) Hemp, Flax, Barley, Wheat, Rye, etc.
The paper goes into the mixed cultivation practices common to the area (except the hemp and the barley being monoculture crops), and a bit about the types of tools used.
Which suggests that Rutabagas were not used prior to 1600 in Western Europe, but the Russians may have been eating them - though likely they came about accidentally.