Ivy Zombies were an irregular mutation produced by Plant 43 via infecting humans with its seedlings.
During the Raccoon City Destruction Incident, Umbrella's underground laboratory, NEST, was put under lock down due to William Birkin's rampage and the subsequent t-Virus outbreak he'd unintentionally caused. As the lock down suspended all activities within the facility, Umbrella researchers found Plant 43's behavior to be growing increasingly hostile due to the lack of proper maintenance. As the lock down prevented the team's proper maintenance of the creature as well as being unable to produce P-ε gas to contain it, Plant 43 inevitably lashed out, killing many of the team before spreading into the ventilation shafts and adjoining rooms.
As it attacked the researchers, Plant 43 had also implanted them with its seedlings. These seedlings would have then sprouted and developed in the bodies, resulting in bipedal humanoid beings covered in vegetation that could walk and vocalize through clicking noises. These creatures also had large orange bulbs covering their form that were susceptible to conventional firearms, however, only flames were capable of permanently killing them. They were shown to be unaffected by the release of the P-ε Herbicide into Plant 43's environment, although it had successfully killed the larger plant, ultimately stunting development of any more Ivy Zombies.
These creatures would all be destroyed following the NEST facility's self destruct sequence being activated.