Cypripedium arietinum R. Brown

Ram's-head lady's-slipper

The specific epithet arietinum is the Latin meaning "like a ram," in reference to the fanciful similarity of the flower of this species to a ram's head.

DESCRIPTION: Plant small, arising from a rhizome with a fascicle of fibrous roots, 8-30 cm high; several stems may arise from the same rootstock. Leaves 3-5, ovate-lanceolate, plicate, 5-10 cm long and 1.4-3.5 cm wide. Flower solitary, subtended by a lanceolate green foliaceous bract 3-6 cm long by 1-1.5 cm wide. Sepals three (the only native Cypripedium with the lateral sepals not fused, a primitive condition), purplish-brown to brown, often striped with green; dorsal sepal ovate-lanceolate, 12-25 mm long and 5-13 mm wide; lateral sepals lanceolate, 12-20 mm long and 2-4 mm wide. Petals similar in size and appearance to the lateral sepals, 13-20 mm long and 1.5-3 mm wide. Labellum pouch-shaped, inflated, drawn into a blunted conical point below, 1-2.5 cm long by 1-2 cm wide, opening above with inrolled edges and surrounded by a dense white pubescence; white above grading into white with madder-purple venation then to all madder-purple toward the tip of the labellar cone.

Cypripedium arietinum could probably be confused only with other pinkishCypripedium species such as C. acaule and C. reginae. However, it is easily separated from these two: apart from being the only Cypripedium species with 3 sepals, the leaves of C. acaule are always basal, and C. reginae is much larger, with the labellum not drawn out into a point.

This plant occupies three distinct habitats in Wisconsin: sandy jack pine (Pinus banksiana) woods with little or no understory vegetation, white cedar (Thuja occidentalis) bogs, and in white cedar (Thuja occidentalis) woods over limestone and dolomite along the shore of Lake Michigan in Door County.

May 25 to June 10.

Stoutamire (1967) recorded a small bee (Dialictus sp.) pollinating Cypripedium arietinum.

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