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Compass Plant is easy to distinguish from other Silphium species in Minnesota from the deeply divided leaves and densely hairy bracts and stem. The common name comes from the tendency of basal leaves to orient themselves vertically in a north-south direction to avoid the full brunt of the sun.Long-tongued bees are the primary pollinators of the flowers, including bumblebees, Miner bees, large Leaf-Cutting bees, and others. Short-tongued Halictine bees and Syrphid flies also visit the flowers, but they are less effective at pollination. Occasionally, Sulfur butterflies and Monarchs may visit the flowers for nectar. Several species of insects are specialist feeders of Compass Plant. This includes the uncommon Okanagana balli (Prairie Cicada), whose grubs feed on the large taproot, while a Rynchites sp. (Silphium Beetle) and its larvae feed on the flower heads and stems. The larvae of Antistrophus rufus and Antistrophus minor (Gall Wasp spp.) feed within the stems, forming galls that are not visible from the outside. Nonetheless, they attract the hyperparasitic wasp Eurytoma lutea, whose larvae feed on these gall formers. Similarly, the larvae of Mordellistena aethiops (Tumbling Flower Beetle sp.) feed within the stems, while the adults may eat the flowers. The oligolectic aphid Iowana frisoni sucks the juices from the flowering stems.
The inflorescence is very tall and elongated, with yellow composite flowers about 3-4" across. They resemble wild sunflowers in overall size, shape, and structure. However, like other Silphium spp., the small tubular disk florets are sterile, while the ray florets are fertile. There is little floral scent. A mature Compass Plant has 6-30 of these composite flowers, which bloom during mid-summer for about 1ï¿½ months. The seeds are large-sized, but flat and light, and can be carried several feet by the wind. A large central taproot can extend 15 ft. into the ground. A resinous substance is produced by the upper stem when the plant is blooming. This plant can live up to 100 yearsClevinger, Jennifer A. (2006). "Silphium laciniatum". In Flora of North America Editorial Committee (ed.). Flora of North America North of Mexico (FNA). 21. New York and Oxford – via eFloras.org, Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.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.” (Source: en.wikipedia.org)