MARSHLANDS
by Robin Boothroyd
A univocalism is a poetic form that enables the use of one vowel and one vowel only. It was pioneered by Oulipo, a group of bonkers French writers and mathematicians, who believe(d) that linguistic restraint reveals the true nature of the unconscious. Here’s one that only includes A.
***
Marshlands
A jackdaw darts past
a dark landmass
and lands
athwart a black branch.
Gnats swarm.
Stags brawl.
Swans arch.
Hark! A hawk snags a lark.
Sharp claws hack, slash, dash.
Dastardly, a flash hawk snacks.
***
You can read some of my other formal experiments here. Discover more about Oulipo here [French].
The Cold Tap Sings 
You might want to read Perec’s “Histoire du lipogramme” (in the first Oulipo anthology. I think there is an English translation in Motte’s book). He very much didn’t invent the form. As a Sanskrit scholar, I might also note the presence of such restraints in languages outside of the corpus he looked at.
Thanks for the tip! I do want to do some more research into lipograms, so this will be a great help.