Field Guide
Roughly 70 per cent of the world’s remaining exemplars can be found in 48 square kilometres in Manitoba, just north of the U.S. border
About 70 per cent of the world’s remaining western prairie fringed orchids can be found in just 48 square kilometres of southeastern Manitoba
It is the only place in Canada that is home to this rare and unusual plant. And if trends continue, that small patch of land near the town of Vita, Man., may soon be the only site of Platanthera praeclara left anywhere. Only discovered in Canada in 1984, the western prairie fringed orchid was listed as endangered in 1993. By 2016, roughly 70 per cent of the world’s remaining exemplars could be found in just 48 square kilometres in and around this hamlet about 15 kilometres north of the border with Minnesota. The other 30 per cent is disappearing rapidly from several U.S. Prairie states. Some comfort can be taken in knowing that two-thirds of the Canadian population is within the 5,000-plus hectares that make up the Manitoba Tall Grass Prairie Preserve. Still, there is very little reason to be sanguine about the future of this exceptional perennial.
Western prairie fringed orchids are striking: 90-cm-high leafy stems with anywhere from three to 33 big and showy blooms (the scientific name comes from the Latin adjective
praeclarus meaning “very bright”). In Canada, first shoots appear in late May and by late June they’ve developed flower clusters. In mid-july, most mature plants are in full flower, and by early September they are starting to wither. Canadian Prairie summers are short.
Like its house-trained relatives, these wild orchids can be temperamental. The number of plants that actually flower varies wildly from year to year: with an average annual tally in Manitoba of 8,301 flowering stems, researchers located only 763 in 2012, down from 23,530 in 2003. The plant is particular: it requires wet
sandy soil in areas prone to occasional wildfire and is happiest in tall grass, sedge meadows and roadside ditches — all features gradually disappearing from the North American landscape as farms expand, consolidate and industrialize. Overgrazing, enhanced drainage, invasive species and climate change are all threats. Contributing to the wildly fluctuating numbers is the fact that they do not flower until maturity, and that can take up to 12 years. Further, they can be totally dormant underground for a year or more at a time.
The conditions of their existence are rarefied too. The further north they are, the fewer seeds they produce. And from seed to maturity, they depend on nutrition supplied by mycorrhizal fungi in a symbiosis typical of orchids, cultivated or wild.
But here is the truly remarkable thing about the western prairie fringed orchid: its pollination system. Despite its physical beauty, which from an evolutionary standpoint is generally a means to attract pollinators, it does not draw them during the day. Instead, it releases an alluring fragrance after the sun has set when moths are out and about. Not just any pollinating moth will do. First, it has to be able to hover, as there is no place to settle. Second, this orchid has such a long nectar spur (the longest of any North American variant) that only sphinx moths (Lepidoptera: Sphingidae, also known as hawk moths) with the properly protuberant proboscis can draw the sweet liquid — too long or too short, and pollen transfer will fail. Third, the moth must be a of a certain size because, in positioning itself to insert its straw-like protuberance, the sphinx moth aligns and approaches so that the orchid’s viscidia brush clusters of pollen onto its eyes. Fourth, with any luck, the pollen will be delivered via the eyes to a flower of a neighbouring plant, ensuring genetic diversity.
As plant numbers dwindle and patches of available habitat shrink, their capacity to draw and sustain sphinx moth populations diminishes: cross-pollination drops, plant populations dwindle, and the cycle of decline deepens.
This remarkable plant lives up to the entire orchid family’s reputation for being “exotic,” even when native. And for the time being, in Vita, Man., on the eastern fringe of our prairie, the western prairie fringed orchid lives in its native soil.