Actually, two other origins have negatives. Seismics get a -1 penalty to speed, and Rat Swarms are vulnerable 5 to area and close attacks.
Seismic comes with resist 5 physical, the most common type of damage. It does not however have a +2 to a defense. But the resist pretty much makes up for it.
The Rat swarm not only has resist 5 melee/ranged as part of the swarmy-ness, but they have a second trait that makes them not able to be knocked prone.
Plants, where everyone else has a kinda nifty thing that makes them unique, they get what almost equates to vulnerability 5 fire. That's it. They could have SOMETHING else to help make up for this;
Don't need food, just water and sunlight.
Aura 1 of difficult terrain to enemies
Take half level damage to heal an adjacent ally one level.
Can be pushed, pulled, or slid when second winding.
Blind vision / tremor sense
An At-will instead of an encounter.
ANYTHING!
As a GM, I let anyone who rolls plant to roll again if they want. As a player, I be as reckless as possible until the plant dies, and I get to re-roll. I fully agree, completely under-powered.
You can say that Gamma World is not about balance. It's true. There are some great origins out there. Demons have a minor at-will attack/teleport.
AI's are less dazed and stunned. Reanimated regenerator would heal 1.5 level +1 hp a round and you could start at 30 HP. There are also some that don't really shine. But the whole point is, when it comes to origins, there's a few great, many good, some okay, and ONE bad.
Sorry for resurrecting a dead thread, but it needed to be said.