Question

What genres does American literature include?

Answer 1

You really should read this work published by the American government about American Literature. You can download it for free in PDF format. Please, use the link below to have access:
http://www.america.gov/publications/books/outline-of-american-literature.html

Answer 2

This could be helpful to
http://www.csustan.edu/english/reuben/pal/TABLE.HTML

In particular the appendices on poetry, fiction, drama (and also on folklore and humour, satire and wit)
http://www.csustan.edu/english/reuben/pal/TABLE.HTML

Answer 3

A good definition of what genre is: http://academic.brooklyn.cuny.edu/english/melani/cs6/genres.html