Actually, statistics indicate it's probably the soybean. although a legume by classification, it's still considered a vegetable, especially the edible variety. But the consumption of soybeans in all forms of use greatly outpaces others. With the initiation of it's use in <i.bio-fuels recently, that consumption will only increase exponentially...
Well I would agree with the humble pea, if you regard the pea as a pulse, including lentils etc. Then that means it is not the most widely used vegetable, but pulse.
I'd go potatoes if classed as a true vegetable. However, the pea could be as nobody eats just one do they?! Hence commonly used. Plenty of peas in a portion!
Agree with Clanad - soya bean.
Under the traditional classification of everything into 'Animal, Vegetable, and Mineral', tubers, legumes, cereals, etc, are all subdivisions of 'Vegetable'
I don't eat ANY peas let alone one. Nasty, horrible things. I think peas as well. They get everywhere. Soups, stews etc., whenever you go for a meal you nearly always get peas as part of your veg. Peas - eugh - almost as bad as sweetcorn.