Phytos are zombies that are half-plant and half zombie.
They live in a greenhouse in Minneapolis where they act with a hive-mind. They are all connected via vines and can feel each others pain. They live off of random people that go into the greenhouse in search of the mysterious Batch 47.
Generally slow to react, the Phytos blended into their surroundings, usually immobile, but like spiders in a web, reacted when the vines linking them were disturbed. A distinct advantage of the vegetative phytos was the lack of dependence on their brains. Shooting them was ineffective and even a direct shot through the head would not bring them down as each was merely an extension of the network of phytos. Complete destruction of the head seemed effective in immobilizing a single phyto however.
Phytos respond to Murphy but can also transmit feelings of pain and anger to him. The Phytos, whilst mostly docile around Murphy, seemed to be controlled by a central zombie at the core of Batch 47. This zombie appeared dormant until he was disturbed by Murphy picking material from the plant nearby at which point it awoke and became agitated, this causing a violent reaction in the generally slow moving Phytos. This core Phyto did not seem to respond to Murphy's control and could only be influenced at all when Murphy directly grabbed the vines intertwined with it, and even then, it was a losing battle on Murphy's part.
It can be assumed that the Phyto strain of zombies were destroyed when the greenhouse containing them was burned down.