Annuals, 40-150 cm. Stems erect to ± procumbent, hispid, hispid-hirsute, or hirsute. Leaves mostly cauline; mostly opposite; petioles 5-9 cm; blades deltate to ovate (sometimes constricted near middles, subsp. praecox) , 3-9 × 2-7 cm, bases cordate , cuneate, or trun-cate, margins serrate to serrulate, abaxial faces hirsute to hispid, usually not gland-dotted. Heads 1-3. Peduncles 15-40 cm. Involucres hemispheric, 13-18 mm diam. Phyllaries 30-39, lanceolate, 9-15 × 2-4 mm, apices short-attenuate to short-acuminate (subsp. praecox), abaxial faces hispidulous to hispid-hirsute. Paleae 6.5-8 mm, 3-toothed (middle teeth acuminate, equaling or slightly surpassing discs, apices puberulent or bearded, hairs whitish). Ray florets 11-16; laminae 16-26 mm. Disc florets 35+; corollas 5-6 mm, lobes reddish; anthers dark, appendages purplish red (style branches reddish). Cypselae 2.5-3.3 mm, ± villous; pappi of 2 aristate scales 1.2-1.5 mm.

The taxa of Helianthus praecox were placed as subspecies of H. debilis by C. B. Heiser (1956). They were separated later, primarily on the basis of crossing results (Heiser et al. 1969). The subspecies appear to form a grade between H. debilis and H. petiolaris.