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Word of the Week: Poikilohydric
April 18, 2018 by Sammy Tangir

Welcome to Word of the Week! Stay tuned for a new word each Wednesday to amp up your nature vocabulary!

A close up look at moss, a poikilohydric organism. In the image on the right (photo taken through a magnifying lens) you get a view of the moss's sporophytes (spore-producing part of the moss).

Poikilohydric [POI-kee-loh-hi-drik] (adjective): When an organism's water content changes with the moisture in the surrounding environment.

Poikilohydric organisms have no means to prevent desiccation (drying out completely). Some of the most well known poikilohydric organisms include mosses, lichens and waterbears (a very hardy microscopic organism). When it is rainy and damp mosses, for example, soak up water. Doing this allows them to photosynthesize and grow, but when the environment dries up, so does the moss. Amazingly, mosses and other poikilohydric organisms are able to survive desiccation and live in “water stressed” areas where other herbaceous plants would be unable to survive! 

A downside of poikilohydry for moss is that when the organisms dry up and they are unable to grow, so their growth is tied to periods where they have access to water. Next time you see a crack in your sidewalk look closer! On the driest summer days the moss might look dead, but they will rehydrate once it rains! 


“The process allows these beings to hover at the boundary between life and death, and is still a profound mystery that is continually played out in the mosses beneath our feet”- Robin Wall Kimmerer (Gathering Moss, p.60)

Sammy Tangir - Sammy is a serious nature nerd and especially enthusiastic about plants! When she is not thinking of next week's nature word, she is working as an outdoor educator and practicing her wood carving skills.

Sources are listed below.

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