How are these vegetable grouped in your language? Are some of them considered varieties of the same vegetable?
Cabbage: cavolo / cavolo cappuccio (lit. hood cabbage)Chinese cabbage
>Napa cabbage: cavolo cinese (lit. Chinese cabbage)
>Bok choi: bieta cinese (lit. Chinese chard)
Cauliflowers: cavolo / cavolfiore (lit. cavolo + fiore = "cabbage + flower" - cognate with English cauliflower)
Both cabbage and cauliflowers are cavolo. To distinguish them, cabbage is cavolo cappuccio, while cauliflowers is cavolfiore.
While Italians are not familiar with Chinese cabbages, those are the Italian names used in the market of the Chinatown of Rome.
Mandarin Chinese (Northern usage):
Cabbage: 卷心菜 juǎn xīn cài (lit. rolling-heart vegetable), 圆白菜 yuán bái cài (lit. round "white vegetale", see below), 洋白菜 yáng bái cài (lit. Western "white vegetale"), 包菜 bāo cài (lit. wrapped vegetable), 包心菜 bāo xīn cài (lit. wrapping-heart vegetable), 甘蓝 gān lán (lit. sweet blue . But scientifically, it means brassica oleracea)
Chinese cabbage: 白菜 bǎi cài (lit. white vegetable)
>Napa cabbage: 大白菜 dà bái cài (lit. big white vegetable) - but often called simply 白菜
>Bok choi: 小白菜 xiǎo bái cài (image, lit. small white vegetable) || 油菜 yóu cài (image, lit. oil vegetable) - they are called the same in English, though I consider them different vegetables.
Cauliflowers: 菜花 cài huā (lit. vegetable flower)
Broccoli: 西兰花 / 西蓝花 xī lán huā (lit. Western blue flower)
It makes sense that if in the West white vegetables are called "Chinese cabbage", then cabbages are called "Western white vegetable" in China.
So cabbages and Chinese cabbages are grouped together.
If using a different word, then cabbages are grouped with broccoli (considered Western and flowered kind of cabbages).
Napa cabbage and bok choi are grouped together. But while napa cabbage can be called simply "white vegetable", for the bok choi you have to specify "small white vegetable". Since "bok choi" comes from the Cantonese pronunciation of 白菜 this can be considered a false friend.
This is the usage in Northern China. Not sure about other regions.
Cabbage: 椰菜 (lit. coconut vegetable ?)
Chinese cabbage: 白菜 (lit. white vegetable) (?)
>Napa cabbage: 大白菜(lit. big white vegetable), 黃芽白 (yellow sprout - white ?), 紹菜 (Shaoxing vegetable ?)
>Bok choi: 白菜 (lit. white vegetable) (?)
Cauliflowers: 花椰菜(lit. flowered coconut vegetable)
Broccoli: 花椰菜(same as cauliflowers)
Here I'm not sure. If someone knows the proper Cantonese words, please correct me.
Cauliflowers and broccoli are the same thing. They are distinguished only by color. They are also grouped together with cabbage, considered "cabbage with flower", same as Italian.
For the Chinese cabbage, if one says simply "white vegetable" (without specifying big or small) he's referring to the small one (bok choi, from which the English word comes), contrary to the rest of China.
Southern Wu - Wenzhounese (W) & Qingtianese (Q)
Cabbage: 球菜 W: /dʑaʊ tsʰe/ Q: /tɕɨʉ tsʰe/ (lit. ball vegetable)
Chinese cabbage: 白菜 W: /ba tsʰe/ Q: /be tsʰe/ (lit. white vegetable)
>Napa cabbage: 大白菜W: /da ba tsʰe/ Q: /da be tsʰe/ (lit. big white vegetable) - but often called simply 白菜
>Bok choi: 小白菜 W: /ɕiə ba tsʰe/ Q: /ɕiœ be tsʰe/ (lit. small white vegetable) || 油冬菜 W: /ʝaʊ toŋ tsʰe/ Q: /ʝɨʉ ɗoŋ tsʰe/(lit. oil winter vegetable), 香菇菜 W & Q:/ɕi ku tsʰe/ (lit. mushroom vegetable - they are often cooked together with mushrooms)
Cauliflowers: 花菜 W: /fu tsʰe/ Q: /hu tsʰe/(lit. flowered vegetable)
Broccoli: 花菜(same as cauliflowers), to be more specific: 绿花菜 W: /lo fu tsʰe/ Q: /liœʔ hu tsʰe/ (lit. green cauliflowers)
Maybe because this is my native language, I find it the most logic way of grouping: cabbage with Chinese cabbage, cauliflowers with broccoli*.
As Mandarin, 白菜 alone means napa cabbage, not bok choi.
小白菜 is the same as Mandarin, while 油冬菜 and 香菇菜 are the synonyms for the Mandarin 油菜.
*I know that scientifically they are all Brassica, but actually I don't perceive any similarity between cabbages and cauliflowers. And aren't cauliflowers and broccoli different only in color?