Its a kind of knotgrass. It is found in different parts of world. In my photograph.. its a asian variety. Annual,spreading seed,it is not a grass as the name suggest but is a member of family "polygomaceae".
(A) Leaves- have no stalk and are almost rounded at the ends. Sap can be irritant to skin.
(B) Flowers- appear from jun to october as cluster of small pink flowers at the angle of leaf and stem.
(C) Height- upto 50-60 cm, but in open ground it is usually prostrate,scrabling over the surface
(D) Seed- can lie dormant for sometime, so allowing a fellow period before planting or sowing should allow germination and the weeds can be removed.
(E) Weedkillers- paraquat,diquat (1 year and 315 days ago)