Green Worldz

Green Worldz is a manga series by Yuusuke Oosawa. It was serialized in Manga Box.

Plot
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!