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Gentiana algida (Gentianaceae)

Plant of the month (©Pierre Laszlo, all rights reserved)
Gentiana algida (Gentianaceae)

Motion in plants is well-known as an insect-trapping, nutritional tactic ; or as a defense mechanism against herbivores. It has other uses, too. Protection of the reproductive apparatus is a fundamental need, which Gentiana algida illustrates. 
The adjective algida means "cold" in Latin. The common name is  "arctic gentian." It is found in cold, mountainous parts of Asia. It is also found in North America, southeastward of Alaska and the western Yukon. It is found as far south, as enclaves in the alpine regions of the central and southern Rocky Mountains, Wyoming in particular.  
Meadows and fellfields are its usual residences, above 3,000 m (10,000 ft). 
Typically found as ground-hugging tufts, it has a solitary stem as short as 2 cm. One to three flowers gather in a simple terminal cyme. The conspicuous, typically white flowers, are near 5 cm in length. Their five petals unite into a corolla in the shape of a funnel. The leaves resemble grass. 
These conically-shaped, vertical flowers serve as their own weather stations and shelters. They close in anticipation of an approaching thunderstorm. Frequent afternoon thunderstorms are indeed summer characteristics of the region, during August especially. When a thunderstorm looms, flowers close within minutes. They reopen after the sunlight returns. When the air temperature decreases, the corolla closes, at a rate of about 10 % / mn. 
This answers the questions, when? and how? There remain the questions why?, to what purpose? The main stimuli for corolla motion are drops in either or both solar radiation and air temperature that both announce a threatening thunderstorm. 
The plant movement protects the reproductive apparatus from rainfall. Precipitation might affect pollen dispersal in Gentiana algida through a reduction in pollen numbers or a change in pollen consistency, rain might also reduce or annihilate pollen dispersal by interfering with flower–pollinator interactions. Manipulated (coned) flowers that were artificially forced open during a rain event were observed to gather and retain rainwater for several hours, with attendant diution of the nectar.
Toward the end of his life, Charles Darwin with the help of his son Francis, worked on plant movements. It was one of his last published books. Darwin described how plants respond to external stimuli, as examples of natural selection. This high-altitude plant, a remarkable adaptation to local climactic conditions, bears him out.