I don't think that Chenopodium is commonly called "sheepsorrel" - though I could be wrong. I have called it "lambs quarters" since I was a child, and I have also heard it called "goosefoot". Wikipedia lists both these as common names as well as a few others - but sheepsorrel is not among them.
On the other hand, I have heard the name "sheep sorrel" applied to Rumex acetosella. The Peterson's Field Guides do for one. Wikipedia does for another.
I suppose that if there is a region somewhere where Chenopodium is called "sheepsorrel", it really serves to underscore the importance of binomial names. --Jomegat 12:49, 27 September 2007 (UTC)