Its just my job to inform.

Identification of a particular weed is not nearly as important as knowing the proper herbicide to use. These 2 different weeds are both Dicots, which means a Selective post-emergence herbicide will knock them down. Round Up is a herbicide but not a Selective Herbicide, I am treating lawns, not barren fields, so I want the Turf Grass, a Monocot to survive.

My company by choice uses a product called Momentum.  I have used this product for several years now and quite happy with the results.

The above image is a weed called Black Medic, the one below that is Oxalis or as some call it shamrocks. These 2 are similar but after you see them they are quite easy to identify. Both have similar shaped leaves,  however Oxalis is a heart shaped and Black Medic is oval; the seed pod on Black Medic is the give away; Oxalis has a flower, not a seed pod; though both are yellow.
The bottom picture is of Clover, white and pink clover are both the same plant, one simply has a pink flower rather than a white one, I have yet to see a Yellow Clover. Here is where the leaf shape will help identify this weed. Oval shaped, Black Medic also is oval but the growth habit of Clover is close to the ground where Black Medic grows more upright. 

and now you too know some of what I know and use on almost a daily basis.