Plant 42

Plant 42 was a large plant infused with the t-virus, and was originally part of an experiment on botanic subjects by Umbrella researcher Henry Sarton. The name location that the plant was growing on was "Point 42" of the Umbrella Residence (Plant 42 would literally mean "Plant at Point 42").

History
When the T-virus outbreak contaminated the Umbrella facility in the Arklay Mountains, a specific plant growing at "Point 42" of the facility was exposed to the virus, thus undergoing massive metamorphosis.

Because of the drastic changes, which also included its dramatic increase in size, it is unknown even by researchers and observers what kind of plant it originally was. With a massive flower-like nucleus protected by distorted petals and extremely powerful vines, Plant 42 immensely grew to invade the Residence, using its securely protected vines to feed on the T-virus altered water of the Aqua Ring beneath it. It had also acquired further nutrients by using its vines to capture its prey, when given the opportunity, and drain them of their blood. It was confirmed by Henry Sarton's report that there were several researchers who were killed by Plant 42. When Plant 42 exposes its nucleus or internal organs by opening its petals, it becomes much more aggressive towards trespassers.

As noted in a chemistry report lying around in the Residence, the Plant's mutations also made it singularly weak to a particular chemical codenamed V-Jolt or UMB № 20. Exposing the roots of the plant to the toxin dries them up and weakens it considerably.

Encounter
When playing as Jill Valentine and concocting the lethal V-Jolt and throwing the vial containing it to the roots, she is trapped by the withering Plant and saved by a Flamethrower-wielding Barry Burton. In Chris Redfield's case, he cannot fabricate V-Jolt on his own. Depending on whether or not you get the serum for Richard Aiken on time, you will either have to fight the plant in the traditional way, or if Richard dies of poison, a cutscene will play in which Chris is trapped by the vines of the Plant, and the player takes control of Rebecca Chambers, who is forced to prepare the chemical and administrate it to the roots in order to weaken the Plant enough to allow Chris to battle it.

The existence of Plant 42 pushed Umbrella scientists to further research Plant-based B.O.W. development. The result was the smaller, more mobile "Plant 43", also known as "Ivy", which was encountered in Raccoon City during the outbreak.

Trivia
The Ritual plant in resident evil 4 is maybe a tribute to plant 42 as they are considerably similar in appearance.