hemp sesbania
Sesbania herbacea                                         

Identifying Characteristics:

Seed:  brown, mottled with black, two times longer than wide 

Seedling:  cotyledons lance to spoon-shaped, first true leaf simple

Mature Plant: fibrous from taproot; erect, tall, branching stem; alternate, pinnately compound leaves; yellow inflorescences; legume fruit

Method of Propagation: seed

Life Cycle: erect annual herb

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