Even the etymological family is a mess. They all backtrack to Latin caulis stalk, stem, cabbage stem; but even in closely related language varieties they might mean different plant varieties, like
Galician, general - col wild kale/cabbage/whatever, collards
Galician, south - couva~couve kale
Portuguese - couve kale
Spanish - col cabbage
...and of course people had to reborrow the word from Latin to refer to stems in general, to make the thing even messier. (e.g. PT "caule" stem)