It's not that Boron has only four true crystal structures that makes it interesting, the real deal is at the fact that Boron is very hard to predict. It disobeys all the rules of periodic table. Artem Oganov from State University of New York at Stony Brook discovered a never observed allotrope of boron just recently and this may not be the last one.
Ken Chang wrote about this and mistakenly mentioned three forms not including the study he was writing about. He corrected it soon after but it was long enough to get caught by Conan O'Brien.
Check out the video on Conan's take on the matter.