Well then we are entering the territory of the wild lettuce family. I don't think anyone mentioned a smell from the leaves, but a milk colored substance coming out of the stem when you break one (or not) would be a featu to look for to help narrow down what you might have. Wild lettuces are a large family of plants, so finding your particular weed might be tough, but look at some pictures of them or sow thistles (not quite the same as wild lettuce but similar). Here is a link that might be useful:

I don't know how much of your garden is planted so far, but if you feel like you can't control the weeds in the whole area, I'd consider limiting the planted area to as little as a quarter of the space. By careful weed management in a smaller area you may actually increase your yields compared to gardening the whole space under heavy competition from whatever weed you've got-- johnsongrass is a good guess. Virginia tech has a weed identification site (google ipm weed virginia and the link should pop up). The drawback of trying to garden the whole area and failing to get the bad weed problem under control is that you'll be perpetuating and increasing your weed population for next year. I have a very productive garden that's approximately 25x25. The perennial weeds still kick my butt this time of year (my own pest is nutsedge right now... I won the war with bermudagrass), but with constant vigilance hand-weeding can usually be successful in a small space. If you can limit your garden to only a portion of the space, then you could repeatedly till the rest of the area (tilling once just increases the problem. If you till repeatedly at two week intervals eventually the roots run out of steam and weaken) or mow or graze animals on it. Whenever possible, remove the roots and stems or at the very least leave them on top of the soil to dry out instead of leaving them buried to regrow. Good luck! I wish you had turnips instead! Here is a link that might be useful: Johnsongrass eradication

>>they are soooo good!!! Yes,..it might choke you a little. These things grow like weeds here,..got several my own seedlings, early ripening, are black right now. They might soon be recognized as a super fruit, for their healthy properties. I'm always looking out for these, something out of the ordinary sweet tasting chokecherry, ..this spring I grafted one from someone claiming it's sweet,..next year I might find out. If you have a sweet tasting one, I sure would love some scion.

You can get a variety of 'cross species' crosses in the Brassica and some of the more interesting types are a direct result of one of the various '3 way' interspecific crosses possible. I've attached a link to a chart that shows them. B. Juncea (Mustard Greens) are a result of a cross of B. Nigra (black mustard) with B. Rapa (turnips, field mustard, turnip mustard). B. Napus (rhutabaga, rapeseed)a cross of B. Rapa with B. Olerica (cabagges, kales, broccoli, etc. as above. B. Carinata (Abyssinian Mustard) a cross of B. Olerica and B. Nigra. Who knows what other crosses they have had. The Brassicas are a bit "loose" with their genes... ;-) So while I'd guess what you have is a wild "turnip mustard" it could just as easily be a strange cross... You had turnips (B. Rapa) and a collard (B. Olerica) so if they crossed you could easily have gotten a new variety of Rhutabaga. I'd trial it and see if it was any good. Pretty much all the candidates are edible in one way or another... Here is a link that might be useful: