Books and Beyond: The Greenwood Encyclopedia of New American Writing is a four volume collection of well-researched articles on various types of contemporary literature. (Edited by Ken Womack, Greenwood Press: Westport, Connecticut & London, 2008).

I'm pleased with my own article on flash fiction (about 8,000 words)
and impressed with all the other articles. Each of the 80-plus articles by experts in the type are carefully researched and all follow the structure of Definition, History, Trends and Themes, Contexts and Issues, Reception, Selected Authors, Bibliography, and Further Reading (each article is 7,500-plus words).

This encyclopedia of contemporary literatures and reading practices merges conventional forms of text with unconventional types in a myriad of ways and each article provides the finer points of each type.

Here are just some article titles I find fascinating (including in-depth
discussions of many types of writing I was not that familiar with).

Magical Realism
Terrorism Fiction
Verse Novels
Transrealist Fiction
GLBTQ Literature
Language Poetry
Latino American Literature
Philological Thrillers
Road Fiction
Asian American Literature
Academic Fiction
Arab American Literature
Cyberpunk
Native American Literature
Literary Journalism
Manga and Anime
(plus many more articles I've not explored yet).

The retail price of this four-volume encyclopedia might be outside the budget of a lot of writers, but asking the local library to order the collection is also a possibility. Writers in general would gain a lot from reading these articles.

Now I'll get back to exploring it more myself. More info another time.