Those "plants" are often referred to as "Mexican Security" - stealing the car will lead to a very "sticky situation" (I got a few around my windows to deter entry). On the other hand, the fruit is known as a "prickly pear". They have a lot (yes, it is two words) of seeds but are very delicious (if you use proper preparation to remove the "prickly" parts). And with that same proper preparation, you can make an excellent Margarita.
Jim
