Pretty but odiferous miner's socks attract flies

By Jeff Mitton

The name of bistort, one of our alpine wildflowers, is amusing.

I am not referring to the Latin binomial (Polygonum {formerly Bistorta} bistortoides) nor "bistort," a simple contraction of the former name of the Genus. "Miner's socks" is the most distinctive and descriptive name and it tickles my humor.

Miner's socks are found in a variety of alpine environments, and in some places they are the most conspicuous of the flowers. A single, slender stalk supports a dense, columnar cluster of small white flowers.

They don't look like a miner's socks, but they smell like them. Actually, they smell more like rotting flesh, and for good reason.

They don't look like a miner's socks, but they smell like them. Actually, they smell more like rotting flesh, and for good reason.Communities of pollinators change with elevation. At the edge of town, honey bees are probably the most common pollinators.

They were introduced to North America from southern Europe in the 1600s.They are not adapted to higher elevations and are unable to reach the alpine, so these recent immigrants had nothing to do with the evolution of the distinctive fragrance of miner's socks.

At lower elevations, a wide variety of solitary bees, bumblebees, flies and butterflies serve as pollinators. Flowers competing for the attention of these pollinators attract them with bright, conspicuous flowers, sweet fragrances and nectar. With increasing elevation, the numbers of species and the densities of populations of solitary bees decline.

The alpine, or area above tree line, is a harsh environment, characterized by cooler summer temperatures, high winds and a short growing season.

Consequently, alpine wildflowers are short to minimize buffeting by the wind — a number of them grow as cushion plants, just a few inches tall. Most are perennials, for some of the summer growing seasons are remarkably short, and those years would select against plants that need to complete their life cycles each summer.

Many of the perennial plants can store energy in their root systems so that they can grow quickly in early spring or to produce flowers and seeds.

The harsh environment of the alpine also impacts the community of pollinators. Many of the solitary bees found in the subalpine are absent or rare or absent in the alpine. Most of the bees seen above tree line are bumblebees, which have a higher tolerance of low temperatures. So the alpine pollinators are predominantly flies and bumblebees.

My colleague, Dr. Carol Kearns, is an authority on both bumblebees and pollination biology. From extensive experience in the alpine she reports that flies are more abundant than bumblebees, and when the weather becomes chilly and breezy, the majority of the bumblebees stop flying, leaving the job of pollination to flies.

In a study of pollinators in western Colorado, she documented 83 fly species visiting flowers above 9,900 feet.

Flies are attracted to flowers, for they will consume either pollen or nectar. But flies are most attracted by the smells of rotting flesh and feces, where they lay eggs.

From the perspective of a plant needing to attract pollinators in cool breezy weather, reliance on bumblebees is risky, while reliance on flies is much safer. Consequently, plants that rely most heavily on flies will catch more pollinators with a putrid stench than a sweet fragrance.

Miner's socks, or bistorts, clearly rely most heavily on flies for pollination.

Miner's socks have taught us something about pollination biology, but they might have also shown us something about longevity as an adaptation to the alpine.

Oren Pollak received a master's degree at CU for his work on the ecology of miner's socks. He discovered that the caudex, the basal stem structure from which new growth arises, retained bud scars from each year, providing a way to estimate the age of bistorts.

When he compared bistorts on the top of Niwot Ridge (above 11,200 feet) with bistorts growing at 9,500 feet, he found that plants on top of the ridge were up to 74 years of age and were twice as old as at lower elevation.

This suggests that the harshness and unpredictability of the alpine may favor long-lived species, just as they favor perennials over annuals.

Jeff Mitton, mitton@colorado.edu, is a professor in the Department of Ecology and Evolutionary Biology at the University of Colorado. This column originally appeared in the Boulder Camera.

Nov. 7, 2014