The one with three lobes are commonly troublesome in lawns. It is edible with a sourish taste. Itsfruit is a little lady's finger-like pod which spreads the seeds. It isa runner. The other one seen in the middle is with dark green tiny leaves. Both are annoying if left unattended. Anybody ID them for me?
Not true shamrock though, but an oxalis... Oxalis stricta, I think. The most common oxalis, it will have tiny yellow flowers. You are right, the leaves are edible, and make a nice addition to a salad with their sour taste. I leave a few in my garden to do just that, but they are easliy weeded out, having rather weak stems and roots. Try to get them out before they seed, or you will have millions more!
As for the other, I am not sure, but it looks like chickweed (Stellaria media) or one of it's close relatives, anyway. Maybe mouse-ear chickweed. it will have white five petalled flowers, but the petals are so deeply divided they look like ten. Chickweed is also edible, lightly cooked as a pot-herb.
Redrose, I think one of the common names for Oxalis is shamrock, but true shamrock is a lot more like clover, no relation at all! I can't remember the latin name for true shamrock, although I have an herbarium specimen around here somewhere... :)
Oh, we've got the 3-leaved one here! It IS Oxalis stricta I believe, but I've always called it pickle plant as the pods taste tart like dill pickles. (Linnea, you beat me to it! Guess you gotta' wake up PRETTY early on this forum. ;-)
BTW, the true Shamrock is a type of clover, Trifolium, white clover, I think. Linnea's right about one common name for Oxalis being shamrocks, also. Anything that resembles clover is commonly called Shamrocks.