Plutonium Bloom was "born" near a secret Russian nuclear reactor, a poorly shielded one at that.
Moss lichen and small scrub after being exposed to hard radiation eventually began to bond together into the creature you see before you.
Over time the creature began to think for itself and make more concerted efforts to enhance survival.
It wanted to live.
Driven by the hard radiation from the now abandoned reactor the creatures early attempts at moving beyond the edges of the dangerous radiation cloud were less than successful.
Some thought, an ability she found more useful with each passing day, led her to the conclusion that she would need to store the radiation in order to travel farther.
She manipulated small plants to collect the radiation which she then incorporated into her own body.
It wasn't long before her stores and collecting brought her to critical mass.
More time passes and she learns to control the radiation and use it to rapidly adapt new plants and abilities.