spotted spurge
Chamaesyce maculata                                          

Identifying Characteristics:

Seed:  oblong-quadrangular, pale brown, irregularly low transverse ridges

Seedling:  cotyledons glabrous; red stem, first true leaves opposite, irregularly toothed

Mature Plant:  fibrous roots from taproot; prostrate stem, long, highly branched, red with milky sap; opposite leaves, simple; cyathium inflorescence, solitary at node but appearing clustered; capsule fruit, ovoid-triangular

Method of Propagation: seed

Life Cycle: annual herb

References: 
Bryson, Charles T. & Michael S DeFelice. "Weeds of the South."