I get asked this question a number of times. The answer is that there's a number of ways to determine if something is hybrid..
One quick way is to check the history of it on its wiki page by searching for the word "cultivar," and if it pops up read what it says. (the word "wild" is the best word you can find).
Try to find the number of chromosomes you can determine the degree something is hybrid (less is better)
if it has a pH below a 7 (our blood on average is 7.2) then it's very likely a hybrid. To get an even more accurate reading, if you eat only that food then you can measure the pH of your urine, since some things like citrus fruit actually becomes alkaline after it's in our bodies.
The majority of plants that grow in China that are used in Traditional Chinese Medicine are in fact hybrid, so you have to be careful.