Obviously, this plant had a poor radioactive experience. As just a little baby, it had a happy childhood. A mommy plant and a... Oh right, it was asexual, so just a mommy plant. Still happy.
But one terrible day, a clumsy worker accidentally spilled a vat of radioactive toxins on the ground near it. Then, a mad scientist ripped it out and rearranged
it's molecular structure to resemble a uranium atomic strand. Afterwards, mommy plant told it that it was adopted. And this all happened on the same day.
It was too much to take for the little plant. It became angry, and exploded outwards into a violent, hulking, mawed monster of a plant that attacked everything around it. Rushing off, the plant registered itself at the Bureau of Monster Names, coming out with a shiny, bling necklace that said "Nuclear-Powered Plant". While it was at it, the pet also starred in "Little Shop of Horrors" and received some awards for its performance.
* Bad breath
* Radioactive, can indefinitely power itself and not have to pay utilities