Here’s someone who really likes his wood sorrel: http://bushcraftskills.blogspot.com/2010/07/wild-edibles-delicious-lemony-medicinal.html

Yep… after posting… I figured that it was pepperweed, rather than shepherd’s purse… It’s ok, they’re both edible… Which is more than can be said for that fescue… http://the3foragers.blogspot.com/2012/03/hairy-bittercress.html

I noticed Hairy bittercress in untreated lawns of West Georgia during the week of Oct 14. It is a winter annual. In shaded areas its sprout time may be as early as late August. With cool wet weather it probably sprouted even earlier in N.Georgia. Cardamine hirsuta L. – hairy bittercress http://plants.usda.gov/java/largeImage?imageID=cahi3_003_ahp.jpg Stone nailed it on the oxalis. Yellow woodsorrel: Oxalis stricta L. http://www.turffiles.ncsu.edu/PDFFiles/004168/Woodsorrel_Yellow.pdf. Note carefully the herbicide recommendations for your lawn. Both your weeds could be problems in fescue lawns. As Walter said persistent appplication of a broadleaf weed killer will manage themÉ.but (I’ll add) they will thrive in thin turf. Core aerate and reseed your Fescue lawn every September or October. Oops, times-a-wastin’! How ’bout tomorrow.

I’m thinking shepard’s purse: http://extension.psu.edu/pests/weeds/weed-id/shepherds-purse And one of the oxalis. Maybe you could eat them… Be careful… If you’ve put chemicals on your yard, it’s dangerous to graze on the wild edibles. You are dealing with cool weather plants… Maybe you could leave the grass higher, or Over-seed with winter rye… Plant some trees? Plant veggies or Wildflowers. Like W.R. says, the site and conditions is conducive to their growth… Change the conditions, different plants will grow. Maybe Bobby will chime in here… turf is his bread n butter.

looks like pennywort and something else persistent appplication of a broadleaf weed killer will manage them….but they will come back because the site is conducive for their growth