Leaves basally disposed, the basal leaves large and persistent, the stem with very few to many leaves, but these definitely reduced upward in size; leaves entire to toothed, to deeply cut; plants with definite taproots (except S. brachiatum, S. mohrii, and S. wasiotense). Stem nearly naked, bearing only a few bracteal (very reduced) leaves. Heads relatively small (involucre 6-11 mm high, disk 8-15 mm wide), with 6-12 ray flowers; [of a wide range of mostly dry, often acidic habitats]. Blades of basal leaves divided or shallowly to deeply lobed, with several lobes on each side, about as wide as long, or longer than wide, < 25 cm wide; leaves usually glabrous (or sparsely scabrous) beneath; achenes longer than (or as long as) the phyllaries at maturity; [collectively widespread]. Involucre mostly 1.0-1.5 cm wide; achenes 6-9 mm long at maturity; achene wings < 1 mm wide, the wing tips long acute to acuminate, the sinus between the wing tips V-shaped; [of the Coastal Plain and lower Piedmont from se. VA south to extreme e. GA]

Silphium compositum: Michaux var. compositum. Cp (GA, NC, SC, VA), Pd (NC, SC, VA), Mt (NC, SC): sandhills, other xeric forests; common. May-September. Perhaps worth dividing further into two taxa: S. compositum sensu stricto, restricted to the Coastal Plain and extreme lower Piedmont, and distributed from se VA through the Carolina Coastal Plain to extreme e. GA, a distribution very similar to those of Carphephorus bellidifolius, Cirsium repandum, and Vaccinium crassifolium; and S. collinum Greene, with less deeply lobed leaves, and distributed from se. and sc. VA, nc. NC, sw. NC and ne. AL south to sc. SC, c. GA, and ec. AL. [= K, Y; = C. compositum – F; < S. compositum var. compositum – RAB; > C. compositum – S; > S. orae Small – S; < S. compositum – C, FNA, G, SE, W; = S. compositum ssp. compositum – Z; > S. collinum Greene] Silphium compositum Michaux var. ovatifolium Torrey & A. Gray. Cp (GA, SC): sandhills; rare. May-September. Distributed from se. SC south to c. peninsular FL and FL Panhandle.s

All text taken fromWeakley's Flora