1 Angela: Good morning, Ophelia, Mercutio. So we’re filming the historical scenes this week?
2 Mercutio: Yes, we’re just waiting for Will, then we’ll travel to the set.
3 Shakespeare: Hi everyone. Sorry I’m late. I was just packing some lunch.
4 Ophelia: I’m sure there’ll be something to eat wherever it is we’re filming.
4 Shakespeare: If you like turnips, yes.

Turnips are your basic go-to vegetable for pre-17th century Europe. Potatoes weren't introduced to Europe until around 1570 when the Spanish brought them back from South America, and didn't become common for a few decades after that. Before then it was basically all turnips all the time.

For comedy, it helps that "turnip" is an inherently funny word.

Scientifically, turnips are the root of a certain subspecies of Brassica rapa, a plant species that also produces the vegetables bok choy, choy sum, Chinese cabbage, and field mustard, among others. It's closely related to that other fascinatingly diverse species Brassica oleracea, different cultivars of which give us vegetables as different as cabbage, broccoli, broccolini, cauliflower, kale, Brussels sprouts, collard greens, savoy cabbage, kohlrabi, and gai lan (Chinese broccoli). Yes, all of these vegetables are the same species of plant. And then there's the third closely related species Brassica nigra, or black mustard, which is used for making, you guessed it, mustard.

The really interesting thing about these species is that Brassica nigra contains 16 chromosomes in its cells, Brassica oleracea contains 18 chromosomes, and Brassica rapa contains 20 chromosomes, yet they can all interbreed with one another. When they do:

• Brassica nigra×Brassica oleracea contains 34 chromosomes (16+18). This hybrid occurred in the wild and produced the species Brassica carinata, or Ethiopian mustard.
• Brassica nigra×Brassica rapa contains 36 chromosomes (16+20). This hybrid occurred in the wild and produced the species Brassica juncea, or Indian mustard, also known as brown mustard.
• Brassica rapa×Brassica oleracea contains 38 chromosomes (18+20). This hybrid also occurred in the wild and produced the species Brassica napus, which itself has multiple cultivars, including rapeseed or canola (usually grown for seeds or oil), Siberian kale, and the root vegetable known as either swede (to non-Americans) or rutabaga (to Americans).

The relationships between this complex of six species is spelled out in the Triangle of U.

Honestly, this is the sort of thing that Doctor Moreau would have come up with if he'd been into plants instead of animals.