269. Silphium Linnaeus, Sp. Pl. 2: 919. 1753; Gen. Pl. ed. 5, 391. 1754.
[Greek silphion, an unknown plant appearing on ancient coins of the city of Cyrene]
Jennifer A. Clevinger
Perennials, 20–250+ cm (fibrous rooted, rhizomatous, or taprooted). Stems usually erect, usually branched (terete or square, often vernicose with resinous exudates). Leaves basal and cauline (basal persistent or withering before flowering); whorled, opposite, subopposite, or alternate (sometimes all conditions on one plant); petiolate or sessile; blades (1- or 3-nerved) deltate, elliptic, linear, ovate, or rhombic, sometimes 1–2-pinnately lobed or -pinnatifid, bases cordate or truncate to cuneate, margins entire or toothed, faces glabrous or hairy (sometimes stipitate-glandular). Heads radiate, in paniculiform or racemiform arrays. Involucres campanulate to hemispheric, 10–30 mm diam. Phyllaries persistent, 11–45 in 2–4 series (outer broader, foliaceous, inner smaller, thinner, each subtending a ray floret). Receptacles flat to slightly convex, paleate (paleae oblong, lanceolate, or linear). Ray florets 8–35+ in 1–4 series, pistillate, fertile; corollas yellow or white. Disc florets 20–200+, functionally staminate; corollas yellow or white, tubes much shorter than narrow, cylindric throats, lobes 5, deltate. Cypselae (black to brown) obflattened (± winged, shed alone without accessory structures); pappi 0, or persistent, of 2 awns (± confluent with cypsela shoulders and wings). x = 7.
Species 12 (12 in the flora): North America.
In keys and descriptions here, "plants scapiform" indicates plants with distal cauline leaves notably smaller than basal and proximal cauline leaves, and "plants caulescent" indicates plants with leaves ± uniform in size throughout; "leaves persistent" indicates leaves persisting to flowering time, and "leaves caducous" indicates leaves withering before flowering time.
SELECTED REFERENCE
Perry, L. M. 1937. Notes on Silphium. Rhodora 39: 281–297.
