Pitcher's thistle
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 Cirsium pitcheri (Pitcher's thistle)
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| Cirsium pitcheri |
The Pitcher's thistle (Cirsium pitcheri), sometimes called dune thistle, is a species of thistle native to sand dune shorelines along the upper Great Lakes. It grows endemically only in Indiana, Michigan, Wisconsin, and Ontario. It is listed by the U.S. Fish and Wildlife Service as a threatened species.
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[edit] Niche
Pitcher's thistle is a plant of modest appearance through much of its lifespan; it concentrates most of its biomass in a massive taproot that can be 6 feet (2 m) in length. Its long, narrow, gray-green leaves are protected by spines and dense, silvery hairs. Between 2 to 8 years after germination, the juvenile thistle abruptly matures and sends forth a temporary blooming head of 1 m or more in height. At the top of the blooming shoot is a spectacular effusive flower head, ranging in color from creamy white to very light pink, and guarded by spines. Some individuals may be quite bushy, and produce numerous flowering heads. Usually at least 5 years are required for the thistle to reach maturity. Pitcher's thistle is monocarpic; after flowering once, the plant dies. Seeds do not disperse very far, in fact, entire heads are occasionally buried, producing clusters of seedlings.
The Pitcher's thistle is adapted to life on open, windswept, semi-stable sand dune surfaces. It can flower at any time from mid-June through mid-September, depending on the amount of energy it has stored in its taproot and on local rain conditions immediately prior to the flowering.
[edit] History and identification
The Pitcher's thistle was first identified by Dr. Zina Pitcher, a field surgeon of the U.S. Army station at Fort Brady, located at the present Sault Ste. Marie, Michigan. In an unknown summer at some point in the 1820s, Dr. Pitcher was granted leave to go on an adventure camping trip west of the fort on a sandy shoreline of Lake Superior. While exploring what are now the Grand Sable Dunes of the Pictured Rocks National Lakeshore, Dr. Pitcher discovered a Pitcher's thistle in flower. The physician shipped the specimen to botanists who published and named it in his honor, Cirsium pitcheri.
[edit] Today
The Pitcher's thistle can be found in sand dune locations along the shorelines of Lake Huron, Lake Michigan, and Lake Superior. Two of the largest remaining populations have been identified in the Nordhouse Dunes area of the Manistee National Forest, and within Sleeping Bear Dunes National Lakeshore. In addition, Pitcher's thistle continues to grow and flower in some smaller state parks and private tracts along these lake shores.
U.S. Great Lakes dunal habitat is threatened by invasive species such as spotted knapweed. In addition, the value of most suitable shoreline for real estate development continues to threaten the Pitcher's thistle. The thistle is adapted to live in locations where many people would like to build vacation homes and resorts. In addition, the plant's all-or-nothing reproductive strategy does not synergize well with the overall presence of humans, who are likely to pick the pretty flower rather than allow it to finish its bloom.
