but they are very similar in shape and taste.....and the butter bean is a type of lima...so you are both right....
this is true...and i knew it before i looked it up...
The term butter bean is widely used for a large, flat and white variety of lima bean (P. lunatus var. macrocarpus, or P. limensis[2]).
In the Southern United States the Sieva type are traditionally called butter beans, also otherwise known as the Dixie or Henderson type. In that area, lima beans and butter beans are seen as two distinct types of beans.
Phaseolus lunatus is a legume. It is grown for its seed, which is eaten as a vegetable. It is commonly known as the lima bean or butter bean; it is also known as Haba bean, Pallar bean, Burma bean, Guffin bean, Hibbert bean, Sieva bean, Rangoon bean, Madagascar bean, Paiga, Paigya, prolific bean, civet bean, sugar bean or đậu ngự (Vietnamese).