I'm pretty sure this is pigweed
http://www.sasez.com/wp-content/uploads/wpid-2012-08-02-09.13.02.jpg

It has red on the stalk and roots
http://www.sasez.com/wp-content/uploads/wpid-2012-08-02-09.13.11.jpg

(sorry I don't know how to insert image from mobile)

I'm also pretty sure the flower stalk gives me an itchy throat and makes me sneeze. If so, does anyone know if eating the young leaves might be risky for me?

(edit) the more I research, the more I think this may be a variation of the same thing:
http://www.sasez.com/wp-content/uploads/094-200x300.jpg

Yeah that's Amaranth. It comes in a lot of varieties. I have a friend who is allergic to eating it, but if I were you I would start out by eating a few leaves and go from there. Just test it on yourself. I've been eating A LOT of amaranth greens (as cooking greens) this summer and I find them much better (and freer) than spinach.

Thanks Isaac. I haven't found a good spot to successfully grow standard greens out here yet and I miss spinach. Hopefully over time I'll have lots of the wild versions identified so it won't matter as much. I'll experiment carefully with these

purslane's another good green, and it usually grows in the same climates/locations as amaranth, or at least, on our property it does. I find that purslane is more mild and juicier than amaranth. I generall feed amaranth to the rabbits and pigs, because it has a lot of protein, and I usually don't get around to cutting it until it is big and bitter.

So far I've found 3 things that might be purselane. None have milky sap but none quite match pics and descriptions I've found. One has fat juicy leaves with a butter knife shape, the other had spoon shape, the third is not as fat/thick and has a paddle shape. Plan to get comparison pics soon.