Buckwheat
Semi-upright to upright broadleaf summer annual that grows 2-5 feet tall. Has single, multibranched stems; abundant white flowers; and fibrous, dense roots.
Additional Resources
Buckwheat: Managing Cover Crops Profitably (SARE Handbook Series Book 9) by Andy Clark (2007, 3rd ed.)
Sunflower
This upright, broadleaf (non-legume), warm-season annual grows 2-10 feet tall. Has a taproot and rough-hairy stems. Leaves are mostly alternate, egg-shaped to triangular, and entire or toothed.