Digitaria ischaemum

About

Digitaria ischaemum is a species of crabgrass known by the common names smooth crabgrass and small crabgrass. It is native to Europe and Asia, but it is known throughout much of the warm temperate world as an introduced species and often a common roadside and garden weed. It is an annual grass producing an inflorescence with two or more narrow branches lined with tiny spikelets.

Summary from Wikipedia