The author of the feat posted somewhere at some point, saying "When I submitted it, it was a Metamagic feat with a +X level requirement... I don't know how it turned into a General feat, but I didn't do it!", or something similar.
I can't recall if it was +2 levels or +3 levels off-hand.  But as a metamagic feat, given that druids usually cast SNA spells spontaneously, it would give a spell a two-round casting time.  And, obviously, bumping the spell level up means that you're not handing Wall of Thorns to a 1st level character.
So the feat isn't what was originally submitted by 'Whoever came up with' it 
 
-Hyp.