Green Worldz is a manga by Yuusuke Osawa.
Plants have taken over the planet. In 2017, the vegetation in Tokyo rose up and toppled human society in moments. The few survivors are forced to live in the relative safety of a subway network, but supplies are running low. Join an average high school student named Akira as he challenges the plants in a struggle for survival!
Power of the Verse
The verse has low power, with most characters ranging from Wall level to Small Building level, and the strongest characters possessing Supersonic speed. However, Hybrid Humans have very good levels of regeneration for their low tier.