by Nancy Sather
Among Minnesota plants, the western prairie fringed orchid (Platanthera praeclara) holds the record for official recognition of its rarity—a state and federally threatened species, an endangered species in Canada, and a somber member of the International Union for Conservation of Nature Red List of the planet's most endangered species.
Loss of the more than 90 percent of tallgrass prairie habitat probably accounts for historical loss of this rare orchid. Alarmingly, even in protected habitat, populations have been entirely lost from Oklahoma and South Dakota. Sudden or ongoing declines in populations have occurred everywhere except Manitoba, Canada.
Western prairie fringed orchids have disappeared from most Minnesota counties bordering Iowa. Orchids persist in nine western counties, including Polk, which harbors the largest protected concentration of populations in the United States.
During the past two decades, dozens of volunteers have counted thousands of orchids, documented new populations and dates of emergence, and tracked individuals from seedling to adult. Opportunities to photograph a beautiful plant, contribute to scientific knowledge, and enjoy fellowship in the field are the tradeoff for 90-degree days, drenching rainstorms, hordes of mosquitoes, and the occasional skunk.
Thanks to these volunteers, Minnesota is the only state in which the majority of populations have been consistently counted, with a statewide high of more than 10,000 plants in 1994, compared with just over 4,000 in 2010.
Because western prairie fringed orchids across North America have never been counted all in one year, the highest known count from each site is the only way to estimate the number of remaining plants.
The combined total of 29,000 in the United States and 23,000 in Manitoba, if packed like corn in a typical western Minnesota cornfield, would occupy between one and two acres.
One requisite for a good orchid count is an understanding of where to look for the plants. The majority of Minnesota's western prairie fringed orchids occur on conservation lands in central Polk County where bands of wet prairie and sedge meadows lie between slightly higher beach ridges left by Glacial Lake Agassiz. Although the topographic difference is subtle, it appears to make all the difference to the orchid, which is concentrated in interbeach swales pockmarked with willows, shrubby cinquefoil, and bog birch. Few other plants are flowering in these sunny areas when western prairie fringed orchids bloom in July.
The life of western prairie fringed orchids is intertwined with the lives of their neighbors, particularly the underground symbiotic fungi. Researchers in Canada and the United States have identified two major groups of fungi that provide nourishment to the orchid's seeds and make germination possible. We know that the fungi are not specialists on western prairie fringed orchids. One unknown is whether some of the periodic declines we see in orchid populations due to drought are really reflective of moisture conditions that affect these mycorrhizal fungi.
The future of these perennials is difficult to predict. Most seedlings do not survive. Successful seedlings take six years to mature to flowering. Once mature and able to reproduce, the adult plant sometimes goes dormant, pausing one to three years between flowerings.
Because of these limiting factors, the plant's production of viable seeds is critical. Seed production hinges on pollination by specialized hawk moth species with a proboscis long enough to reach nectar in the bottom of the flower's spur.
These moths fly long distances, drawn by the sweet fragrance the flowers emit at night. If the number of flowering orchids in a population declined, the moths might not be able to pick up the scent. Thus, preserving maximum flower production is crucial to attracting hawk moths. If hawk moths stop visiting a prairie, that western prairie fringed orchid population is doomed.