Make it Himalayan blackberries. Those got introduced here in the late 1800s and they are *everywhere* I've seen berry tangles in Forest Park that are bigger than most houses!

Let's see. English ivy is bad, but not edible. Ditto for morning glory. Plantain will cheerfully grab any bare spots in gardens around here, but it's not terribly obnoxious.

It's not local, but I seem to recall something about osage orange?

Cattails will spread pretty well in the right sort of terrain. And both the heads and roots are edible.

Stretching things a bit, various sorts of bamboo. The shoots are edible, and the full grown plants can be harvested for fiber and construction materials.

If they are going to have anything that grazes (cattle, sheep, goats, rabbits, guinea pigs...) you could always introduce crabgrass.

Very much *not* edible, but something that I bet would do well in the early stages of terraforming are horsetails. They were one of the first plants to colonize land.

Hey, here's a thought. Check the various state dept of agriculture sites for their lists of "noxious weeds". then see which ones are edible or otherwise useful.

Not sure what the equivalent would be in other countries, but if you could find it...