I saw a post asking the same question before. I think it said it was because it is simaler to toxifolia and they don't want to risk it getting in the beaches?
P.S. Does any one know if an emrald crab would eat these or other similar plants?
I think because they grow so rapidly in CA that they become a problem to get rid of. (remember there are no tangs there) I don't think an emerald crab will bother them at all. Tangs on the other hand will eat them like a buffet.