Silphium asteriscus L.

Silphium asteriscus plant

Family - Asteraceae

Stems - To +1m tall, simple to branching near apex, erect, herbaceous, hirsute to hispid-scabrous, from caudex and thick roots and rhizomes.

Silphium asteriscus stem

Leaves - Alternate, short petiolate below, sessile above. Blades lanceolate, to +15cm long, +4cm broad, coarse serrate, acute, scabrous and pubescent above, pubescent below. Upper leaves rounded at base. Lower leaves with leaf tissue tapering at base and creating a winged petiole. Teeth of margins with minute whitish apex.

Silphium asteriscus leaves

Inflorescence - Terminal flower heads in a compact corymbiform cluster. Peduncles to +/-2cm long, hirsute to hispid.

Involucre - To +1cm tall, +1.5cm in diameter. Phyllaries imbricate, ovate-lanceolate, acuminate, to 1.5cm long, +6mm broad, spreading to recurved, pubescent to hispidulous.

Silphium asteriscus involucreInvolucre.

Ray flowers - Fertile, typically 9 or 10. Ligules yellow, to 2.5cm long, 1cm broad, narrowly elliptic to narrowly oblong, with small notch at apex, glabrous. Achenes compressed, winged, 5-6mm long, 3mm broad (in flower), mostly glabrous but with cilia on margins near apex, becoming black in fruit. Pappus absent.

Disk flowers - Disk yellow, +/-1.1cm in diameter. Flower staminate. Corolla tubes to 5-6mm long, yellow, glabrous, 5-lobed. Lobes glandular pubescent. Style yellow, undivided, well exserted. Achenes white, terete, glabrous, 5-6mm long. Pappus absent. Receptacle flat. Chaff 1cm long, 2mm broad, yellowish and acute at apex, pubescent above with some glandular hairs.

Silphium asteriscus flower

Silphium asteriscus diskArrow showing the undivided style of the disk flower.

Flowering - May - September.

Habitat - Rocky open woods, glades, roadsides.

Origin - Native to U.S.

Other info. - This plant can be found in the southern-most counties of Missouri.
There is uncertainty about the taxonomy of this species and two others, S. radula and S. integrifolium, which all share common characteristics. Some authors wish to lump all three species under S. asteriscus, others do not. Further study of the complex is needed. Regardless of the name, this plant is part of a genus which looks similar to the sunflowers, genus Helianthus, but the sunflowers have bifurcate styles and plants of the genus Silphium do not. There are other differences between the two genus but the styles are a major characteristic to look for when trying to ID these plants in the field.

Photographs taken at the Peck Ranch Wildlife Refuge, Carter County, MO., 6-12-03.