You might say that writing found in literature is literary; language like that found in poetry is poetic.
What do you call writing found in essays, or writing like that found in essays?
(Not considering prosaic, to head off certain humorous tangents.)
Is there a word or short phrase better than essayistic?
In addition to pieces of writing originating from or destined for an academic group, here are a couple of items that appear to fall into the same category:
Also see Paul Graham: The Age of the Essay