A long question ! With some research, these seem all to be related (but different) plants in the Genus Allium. Some of the names that you list are just the same plant in a different area . Lists of different plants - Chive - this is a herb used in cooking, usually the smaller leaves are used. - garlic chives, Chinese chives, Oriental garlic, Chinese leek, also known by the Chinese name kow choi. All names for the same thing. You should know this one. - leek. These are quite big. Say the thickness of 2 fingers at least. = Scallion = green onion = spring onion. Also called shallots. Usually used in cooking, chopped up, bigger than a chive, smaller than a leek. However all the names that you listed are common names, so depending on where you are, a person might use the same name for different things. I have tried to group them in commoner categories.

They are all green vegetables with some fairly mild spicy or "onion-like" taste. You'd have to be a "foodie" (a person with a special interest in food, like a cook or a gourmet) to know all the answers. You'll need to look them up yourself, on a cooking-related website or in a cookbook. "chive? leek? scallion? shallot?"--they are all different things. However, if you had a recipe that called for leeks and you had shallots but not leeks, you might well try substituting shallots--they'd taste different, but if leeks work, shallots would probably work. You can ALWAYS get an argument going by asking people "are scallions the same thing as green onions?" You will NEVER get a final answer on that one. Names vary regionally. The exact varieties of vegetables vary regionally. What's available varies regionally.