Out of the standard list I'd say Sylvan and Common.
Hm. I was kind of afraid that's gonna be the case. But some of those can be saved, right? I mean, elves get immunity to sleep and some manner of protection against compulsion effects for free. Would, perhaps, adding a few explicit vulnerabilities (to, say, fire, acid and goats (I know, I know, that one's not a type of energy, but it should be)) help?Also, if you don't want LA, I'll have to space out their plant abilities.