Cypripedium arietinum Ait. f.
Ram's Head Orchid
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Basis for Listing
Cypripedium arietinum has always been considered biologically rare in Minnesota, and the reasons for its rarity are not entirely known. Recently, however, it has suffered a general decline in Minnesota largely as a result of habitat loss from changes in land use. For example, recent clearcutting of Pinus banksiana (jack pine) forests on public and private land in Hubbard County, where some of the largest populations of C. arietinum occur, could compromise the conservation of this species in Minnesota. This rare orchid originally ranged throughout most of the forested region in Minnesota, but recent surveys of potential habitat and historic sites have failed to document any extant populations south of Aitkin County. Cypripedium arietinum was originally listed as an endangered species in Minnesota in 1984, and was reclassified as threatened in 1996.
Like all members of this genus, C. arietinum has 3 petals, 1 modified into a pouch or "slipper." In C. arietinum the pouch is densely pubescent and white with purple markings, which, with a little imagination, looks like the head of a charging ram. It has 2 or more alternate leaves borne nearly to the top of the stem. The lateral sepals are free rather than fused, which distinguishes C. arietinum from all other Cypripediums (Smith 1993).
The Minnesota populations of C. arietinum occur in a variety of coniferous forest habitats. Several populations occur in swamps, bogs, or lowland forests dominated by Thuja occidentalis (northern white cedar), Larix laricina (tamarack), Abies balsamea (balsam fir), or Picea mariana (black spruce). The species also occurs in the drier upland conifer forests that may be dominated by Pinus strobus (white pine), P. resinosa (red pine), or P. banksiana. All these habitats appear to be weakly acidic or circumneutral, but vary in their mineral composition from poor to rich.
Biology / Life History
Cypripedium arietinum is a very primitive species and has a long history in the geological past. Evidence presented by Sing-Chi (1983) indicates that millions of years ago it occurred across North America and eastern Asia. However, scattered remnants in eastern North America and a few populations of a closely related counterpart in western China are all that are left of this previous distribution. It is a long-lived perennial pollinated by a variety of small bees. It reproduces only by seeds, which are spread short distances by the wind.
Conservation / Management
The wide range of habitats occupied by C. arietinum makes it difficult to specify which factors limit its occurrence and why it is so rare. In addition to this, some forest management activities have made it increasingly difficult to maintain stable populations. These include herbicide application, discing and rock raking, use of heavy equipment during the growing season, and conversion of the native plant community to a plantation-style substitute. Full removal of the canopy may also impair the continuance of C. arietinum by increasing sunlight and temperature to the forest floor and thus decreasing moisture and partial shade, which this species requires. Other land use activities in or near this species' habitat that could also potentially cause damage include water level manipulations, development, mining, and agricultural production. Many remaining populations, even in State Parks and state Scientific and Natural Area, are vulnerable to illegal collection by orchid fanciers. This type of poaching is especially unfortunate because the plants do not survive transplantation from the wild (Case 1987).
Conservation Efforts in Minnesota
Several C. arietinum sites occur on publicly owned land where they are protected from most types of land conversion, but several are on private property or public property where they receive no special consideration. The status of several populations has been monitored, providing useful information that can help guide future conservation efforts.
References and Additional Information
Case, F. W., Jr. 1987. Orchids of the Western Great Lakes Region, revised edition. Cranbrook Institute of Science Bulletin 48. 251 pp.
Myhre, K. M. 1992. Results of a rare plant search in Cass County. Minnesota County Biological Survey, Minnesota Department of Natural Resources, St. Paul, Minnesota. 6 pp.
Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis, Minnesota. 320 pp.
Sing-Chi, C. 1983. Two pairs of vicarious species of Cypripedium (Orchidaceae) from eastern Asia and eastern North America. Brittonia 35(2):159-163.
Smith, W. R. 1993. Orchids of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 172 pp.