|Amerorchis rotundifolia at Wagner Natural Area, Alberta, Canada|
Amerorchis is a monotypic genus of flowering plants in the orchid family, Orchidaceae containing the single species Amerorchis rotundifolia (syn. Galearis rotundifolia). It is commonly called roundleaf orchis and small round-leaved orchid. It is native to North America, where it occurs throughout Canada, part of the northern United States, and Greenland.
This orchid is a succulent perennial herb growing from a fleshy rhizome. It reaches a maximum height around 33 centimeters. A single leaf clasps the base of the stem. It is variable in shape and size, reaching up to 11 centimeters in length. The inflorescence is a spike of flowers and leaflike bracts occupying the top of the stem. The plant produces up to 18 flowers at a time. The flower has six tepals in shades of white or light magenta; three are sepals up to a centimeter long, and three are shorter, narrower petals. The spurred, lobed lip of the middle petal is white with magenta spots and sometimes bars. There are two pollinaria, which bear the sticky pollen. The fruit is a capsule.
The plant is native to northern North America, where it is widespread and most abundant at the northern latitudes. It occurs in nearly all of the provinces of Canada, Greenland, Alaska, and the northernmost contiguous United States, including Montana, Minnesota, and Maine.
The plant occurs in arctic and boreal climates. In the northern part of its range it is scattered in several habitat types, and in the southern part it is less common and mainly restricted to moist, shady areas. In the Rocky Mountains of Montana and Wyoming, for example, it can be found along steams and in wet but well-drained limestone soils in shady spruce forests and woods. It is a glacial relict species.
The most important factor in appropriate habitat is a cold substrate. In northern regions it can grow in full sun, while in southern areas it requires shelter. It is sometimes a dwarf plant in exposed areas on tundra. The substrate is usually also moist to wet, but not waterlogged. It is an obligate wetland species in southern areas, and a facultative wetland plant farther north. It also requires calcareous soils with a neutral pH, tolerating only slight acidity.
The flowers are pollinated by insects. In a survey of pollinators in Alberta, the primary pollinator was Osmia proxima, a mason bee. Other pollinators included several hoverflies, such as Eriozona laxus, Eristalis hirta, Eristalis rupium, and Eupeodes lapponicus. The insects were observed probing the flower spur with their mouthparts and then getting the sticky pollen wads stuck on their heads as they pushed into the flower. The tiny, light seeds are dispersed on the wind.
In general, this is a widespread and secure species, especially in Canada. It becomes rare on the southern fringes of its range. Threats to the species include overcollection by orchid hunters and poaching of the plant for use as an herbal remedy.
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- Amerorchis rotundifolia - photos and description. Saskatchewan's Wildflowers.
- Le Blanc, D. Protecting Round-leaved Orchis (Amerorchis rotundifolia) on the Hiawatha National Forest. USDA Forest Service. 2010.
- St. Hilaire, L. R. (2001). Amerorchis rotundifolia (Banks ex Pursh) Hultén (Small Round-leaved Orchis) Conservation and Research Plan for New England. New England Wild Flower Society, Framingham, Massachusetts, USA.