Silphium terebinthinaceum

September 22 2009 189

Prairie Dock in bloom

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 leaf margins are coarsely serrated or dentate. 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 blooming period usually occurs from late summer to early fall, and lasts about a month for an individual plant. 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.

Phenophases

  1. First Flower: Date the first flowers are fully open. When open, you will see the stamens among the unfolded petals.
  2. Full Flower: Date when half or more of the flowers are completely open
  3. First Ripe Fruit: Date when you notice the first fruits becoming fully ripe or seeds dropping naturally from the plant. Ripening is indicated by the berries turning red, yellow, orange, or maroon.
  4. Full Fruiting: Date when half or more of the fruits are completely ripe or seeds are dropping naturally from the plant.
  5. All Leaves Withered: Date when most or all of the leaves that developed this season, have lost green color or are dried and dead.

Information from: www.wildflower.org and www.illinoiswildflowers.info

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