Nabalus altissimus, Tall Rattlesnake-root
Involucre smooth, cylindrical; 5-6 flowers per head. Piedmont only.

Nabalus serpentarius, Lion's-foot Rattlesnake-root
Involucre hairy, with spreading bracts; 8-12 flowers per head.

Nabalus trifoliolatus var. trifoliolatus, Three-leaved Rattlesnake-root
Involucre smooth, with spreading bracts; 8-12 flowers per head. No photo.

These species are no longer found in Delaware. Nabalus albus, White Rattlesnake-root
Nabalus autumnalis, Slender Rattlesnake-root


Sources: The Flora of Delaware, Herbaceous Plants of Maryland.