Honey, we shrank the snow lotus: picking big plants reduces species' height.

Plant collectors have become a force of evolution. The way in which they've harvested a Himalayan wildflower has inadvertently driven the species toward a shorter form, according to a new report.

Traditional healers in Asia have long prized the snow lotus (Saussurea laniceps), which grows only in the eastern Himalayas. The plants bloom just once, at the end of a life spanning at least 7 years. Particularly large blooming plants attract collectors, who consider them to have the greatest medicinal value.

Preferential collection of large specimens is selecting for shorter plants, says Wayne Law of Washington University in St. Louis. In heavily visited flower patches, harvesting has increased with the expansion of roads during the past 40 years or so, and snow lotuses there are only 60 percent as tall as are plants at unharvested sites, report Law and his Washington University colleague

Jan Salick in an upcoming Proceedings of the National Academy of Sciences.

Their findings fit into recent trends in the study of evolution, says evolutionary ecologist Michael Kinnison of the University of Maine in Orono. In Darwin's time, scientists considered evolution "so creepingly slow we probably wouldn't see it." With 20th-century improvements in statistics, biologists teased apart subtle changes in species. Now, Kinnison says, there's growing recognition that species can change measurably during the human life span.

Some studies are documenting ways in which people drive evolutionary changes. Much of the work considers changing habitats, but a few studies have observed effects of harvesting. For example, trophy hunters pursuing the largest big-horned sheep have gradually diminished the animals' size, and fishing fleets may have done the same thing for fish (SN: 6/4/05, p. 360). One study of ginseng found plant size dwindling after generations of harvesting.

Law and Salick compared flower patches of the snow lotus in a protected area on a mountain sacred to Tibetans and on common grounds frequently harvested by collectors. In the protected area, the rare species grew 9 centimeters taller than it did at the other site. Yet a closely related and more common plant, Saussurea medusa, which doesn't attract as many collectors, showed no height differences between the two sites.

The researchers also looked at herbarium specimens from more than a century of collecting. The rare snow lotus species showed a measurable decline in height, but the other species didn't.

Despite its name, the snow lotus isn't botanically related to lotuses. It belongs to the same family as sunflowers do.

The recent change in height might affect the snow lotus in other ways, Law speculates. For example, smaller plants might produce a smaller number of seeds.

Law and Salick's paper "makes total sense to me" says Kinnison. He cautions though that "the challenging part is determining what percentage of what they found is truly a genetic change."