I'm surprised Washington wasn't on there, I'd think the Olympic Peninsula and the Cascades together would have enough plant species, especially considering that Oregon makes it. Same with Alaska.
similar to the megadiverse countries quiz, you'd do well to guess large states with a warm or mild climate or those in/near the tropics. Geographic features that increase the number of isolated ecosystems such as valleys and islands also increase biodiversity.
Ouch I can just feel it now. We have a long clam that is called razorblades, "scheermesjes" (more verbatim translation for those fond of language is shavingknives). Im gonna look your one up, who knows they might resemble eachother.