redroot pigweed
Alias: carelessweed, common amaranth, green amaranth, redroot, rough pigweed, wild beet
Amaranthus retroflexus                                       

Identifying Characteristics:

Seed: ovate, slightly flattened seed; oily, shiny appearance; dark brownish red to black in color; slightly notched at hilum

Seedling:  softly pubescent stem and leaves; egg-shaped, alternate leaves; tip of leaf notched slightly

Mature Plant: erect growth habit; numerous small, green flowers; pointed bracts under each flower; multiple densely crowded spikes

Method of Propagation: seed

Life Cycle: warm-season annual

Similar Species: Palmer amaranth 

References:  Bryson, Charles T. & Michael S DeFelice. "Weeds of the Midwestern United States & Central Canada."