Silphium mohrii

Shaggy Rosinweed Asteraceae

A distinctive and rather handsome North American Silphium, Silphium mohrii, or Mohr’s Rosinweed, is a robust herbaceous perennial with large, lance-shaped basal leaves and stout, upright stems covered from top to bottom in conspicuously shaggy, bristly hairs. The stems branch towards the summit to carry numerous pale lemon-yellow, daisy-like flower heads, giving the plant a wonderfully bold but slightly eccentric appearance. Native to a restricted area of the southeastern United States — principally northern Alabama, southern Tennessee and north-western Georgia — it grows in prairies, clearings, rocky limestone openings and dry, often thin soils. 

The foliage is particularly attractive, with the large basal leaves gradually reducing in size as they ascend the stem, while the dense covering of hairs gives the whole plant its characteristic shaggy appearance. Flowering takes place from late summer into early autumn, when the pale-yellow heads are particularly valuable for bringing height and structure to a naturalistic planting. It is a perennial rather than one of the monocarpic Silphium species, and can form an impressive presence where given sufficient space. 

In cultivation Silphium mohrii prefers full sun and a well-drained, preferably gravelly or rocky soil. It is particularly well suited to prairie planting, dry borders and other naturalistic schemes, and is happiest where the soil is not excessively fertile. Once established it is reasonably tolerant of dry conditions, although good moisture during active growth produces the strongest plants. The species has a relatively restricted natural distribution and is considered of conservation concern in parts of its native range, making it an especially interesting addition to a collection of unusual North American perennials. 

Height: 100–160 cm
Spread: 50–80 cm
Flowering: July–September
Hardiness: H5–H6, approximately –20 to –10°C
Growing conditions: Well-drained, preferably rocky or gravelly soil; full sun. Adaptable but avoid prolonged winter wet and excessively rich soil.
Range: Northern Alabama, southern Tennessee and north-western Georgia, USA. 
Habitat: Prairies, clearings, fence rows, rocky limestone openings and dry woodland habitats, generally on thin or sandy soils. 
Habit: Herbaceous perennial with fibrous roots, large persistent basal leaves and tall, shaggy-hairy stems branching near the top.
Flowers: Pale yellow, daisy-like heads with approximately 10–20 ray florets. 
Conservation: A geographically restricted species of the southeastern United States, with particularly high conservation concern in Alabama and Georgia. (explorer.natureserve.org⁠)
Nomenclature: Named mohrii in honour of the German-American botanist Charles Mohr; the species was described by John Kunkel Small in 1897.