A theory.

[Wooble]

I think that piranha plants aren't plants, they just formed a symbiotic relationship with plants. They're simply just animals.
1. Piranha bones: this implies that piranha plants are mostly flesh with the face holes being their eyes, their spine being the stem, their "leaves" being bone hard, and their vines being blood vessels.
2. Food: they hate mario, but if they don't get him, then they sit upright facing the sun and better photosynthesis happens.
3. Jaw: If trottin' piranha bones have boney jaw hinges, then, normal piranha bones might have them as well.
Please tell me if I need to fix anything!

 

[Fizzle]

Nice theory you got there, and I totally would believe that if I was being introduced to Mario, or if I was a veteran of the series

 

[Wooble]

Nice! What should I change?

 

[Fizzle]

I'd say it's good as is, but if you find more to add to your theory, like a third reason, it would make even more sense in a way