How exactly do you tell Shanghai bok choy, napa cabbage, and rapeseed apart?

Shanghai bok choy, napa cabbage, green vegetables, and rapeseed - these names are more like a north-south dispute, but they are actually the same thing.

It started like this: someone told me to go get a so-called napa cabbage from his car, and I said, isn't the napa cabbage in the kitchen.

Actually, what he meant by napa cabbage was this:

I was completely stunned at the time and said, isn't this big napa cabbage? Actually, what I meant by napa cabbage was this:

Then I got mocked: isn't this green vegetable? Are you stupid?

Feeling humiliated, how could I just take it? Just then a friend nearby said, isn't this rapeseed?

What? Rapeseed? There's actually this name too? Isn't rapeseed used to press oil? It can be eaten too? What came to mind was this:

Although I heard as a child about eating rapeseed sprouts, it seems like it's not the same thing. So I thought about it - after all, some people call me Teacher Junyan, and I can't afford to lose face. From memory, I only remembered that this bunch of stuff belongs to the Brassica family, so I hurried to look up the materials and win my face back.

How many names does this thing actually have? Let's take a look.

Then I casually asked on Weibo, and among more than a hundred replies (the first time I knew my followers were really alive), the names were really all over the place. Here they are:

Shanghai bok choy (most common), rapeseed, napa cabbage, green vegetable, small rapeseed, qingjiang cai (Taiwan, China name), piao'er bei (Sichuan name), small bok choy, xiao tang cai (not sure if it pairs with komatsuna), shao'er cai (seems also a Sichuan or Yunnan name), shiitake vegetable (said to have an indissoluble bond with the dish shiitake greens)... There really are so many names.

Next, let's investigate what this is really about.

Based on everyone's replies and the materials, the following things can basically be confirmed:

Northern "rapeseed" = southern "green vegetable"

Southern "rapeseed" = the one used for pressing oil; northern rapeseed is eaten for its leaves, southern rapeseed is pressed for oil

Northern "green vegetable" = all kinds of leafy greens

Here we have to bring out the Latin names. Everyone knows this is the scientific method.

First, they are all plants of the cruciferous family. This is basically exposed as soon as they bloom - they are all cruciform, and they all belong to variants of the genus Brassica.

Then, the scientific name given in the flora is Brassica chinensis var. chinensis, and the common Chinese names are "small bok choy" and "green vegetable," while in Northeast China it is "rapeseed." Of course, a common Chinese name cannot serve as a scientific name; the scientific name can only be the Latin name.

Shanghai bok choy seems more like a cultivar name. Of course, here it comes: it actually also has a name called Suzhou bok choy.

In addition, jimao cai is actually also Shanghai bok choy when young.