Susan Gates 
Viridian [PDF ebook] 

A virus has swept the world, turning polluting, wasteful humans into peaceful human/plant hybrids called Verdans. More and more people choose the Verdan way, till only a few humans are left. But then the Cultivars rise – terrifying, cruel Verdans, genetically modified to become brutal warriors, who are determined to wipe out what remains of humanity. They turn the Verdan dream into a nightmare. And at their head is the lethal Viridian…
The sequel, Viridian: Venus Angel, publishes October 2013.