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

Canadian Wildlife - - CONTENTS - By Mel Wal­wyn

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.

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