Totally humanoid, but also plant creature. Legs made out of stocks and stems, things like that. Changes depending on the writer and artist. He's gone through a few versions, since it's been around for decades. Right now he's a humanoid plant person.

[He looks over the comic he'd picked up again, noticing the ting bleeding out around his fingers onto the pages. Thinking about Plant Man means thinking green, and now the comic book was turning a bold leafy green color, like spills of green ink over the pages covering the art.] Crap.