IUCN threat status:

Not evaluated

Comprehensive Description

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Description

This plant has a vase-like rosette of large basal leaves that are spade-shaped (cordate). Each leaf has a thick sandpapery texture, particularly on the underside, and is up to 18" long and 12" wide. On young leaves, the upper surface is relatively hairless and shiny, while older leaves become dull and rough. The lower surface is light green and pubescent. The leaf margins are coarsely serrated or dentate. The petioles are about 6" long, rather narrow and wiry, and light green or brown. The overall appearance is similar to a rhubarb plant, except the petioles are more slender. A naked flowering stalk emerges from the base of the plant, ranging in height from 3' to 10' in height. This stalk is green or red, and largely hairless. The upper part of the stalk divides gracefully into a panicle of yellow composite flowers and spherical green buds. Each compound flower is about 2-3" across, and consists of 15-30 ray florets with rather pointed tips surrounding numerous disk florets. There is no noticeable floral scent. The blooming period usually occurs from late summer to early fall, and lasts about a month for an individual plant. Prairie Dock usually blooms later than other Silphium spp. It has a stout taproot that can penetrate the soil to about 12' deep, and may form offsets only a short distance away from the mother plant. The rather light, flattened achenes can be carried several feet by the wind; they are without tufts of hair.

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© John Hilty

Source: Illinois Wildflowers

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