Silphium laciniatum is a species of flowering plant in the family Asteraceae known commonly as compassplant or compass plant. It is native to North America, where it occurs in Ontario in Canada and the eastern and central United States as far west as New Mexico. Other common names include prairie compass plant, pilotweed, polarplant, It is a rosinweed of genus Silphium.
Description
thumb|right|Flower head
thumb|upright|Leaves
This plant is a taprooted perennial herb producing rough-haired stems usually one to three meters tall. The leaves are variable in shape and size, being long and wide. They are hairy, smooth-edged or toothed, and borne on petioles or not. The back of the flower head has layers of rough, glandular phyllaries. The head contains 27 to 38 yellow ray florets and many yellow disc florets. The fruit is a cypsela which can be almost long and is tipped with a pappus of two short awns.
Biology
The common name compass plant was inspired by the "compass orientation" Vertical leaves facing east-west have higher water use efficiency than horizontal or north-south-facing blades.
Early settlers on the Great Plains could make their way in the dark by feeling of the leaves. The gall wasps, especially A. rufus, inject eggs into the stem, an action that induces the formation of a gall in the plant tissue. The larva of the wasp lives and feeds inside the gall, overwinters there, and emerges as an adult the following spring. Over 600 galls can be in a single stem. The galls are internal in this species, and generally not visible.
Other insects found in the plant include several species of parasitoid wasps that attack A. rufus larvae in the galls, the two most common being Eurytoma luta and Ormyrus labotus. Others include Eupelmus vesicularis and species of the genera Brasema and Homoporus. The beetle Mordellistena aethiops lives on the plant, its larvae boring into the stems, and it is attacked by parasitoid wasps of the genera Schizopyramnus, Heterospilus, and Tetrastichus. The Pawnee made a tisane ( herbal tea) with it.
In the environmental classic, A Sand County Almanac, Aldo Leopold devotes much of the July entry to Silphium—its hardiness, but its slow disappearance nevertheless, a harbinger of the fate of the prairie. "It is easy now to predict the future. For a few years my Silphium will try in vain to rise above the mowing machine, and then it will die. With it will die the prairie epoch."
References
External links
- Plants of Wisconsin
- Plants of the Eloise Butler Wildflower Garden