What kind of ship has two mates but no captain?

I once was sap in forest shade, then heat transformed what nature made. Now I may bounce, erase, or roll, a stretchable thing with many roles.

No matter what you say, I'm peak. No cap, except ice on me. When snow sloughs off me, don't trip, My melting streams are pure drip.

The opposite of used, I'm what men are upside down.

The internet if it was exclusively for corn.