What You Should Know
Exidiopsis effusa is a species of fungus in the family Auriculariaceae, and the type species of the genus Exidiopsis. It is associated with the formation of hair ice on dead wood.
This fungus is a saprophyte: an organism that lives on and from the deadwood. In cold and damp conditions, this microbe causes the phenomenon of hair ice. It grows by making a network of hyphae, the mycelium, in wood vessels and wood rays. On the outside of branches and deadwood, it can form white to pinkish-blue colored crusts where the fruiting bodies develop.
Other names: White Hair Ice.
Exidiopsis effusa Hair Ice Forming
The conditions required for the formation of hair ice are extremely specific, hence the relative scarcity of sightings. To form, moist rotting wood from a broadleaf tree is required with the presence of moist air and a temperature slightly below 0 °C. There are many reports on the observation of hair ice, mainly at latitudes between 45 and 55 degrees N in Canada, France, Germany, India, Ireland, Netherlands, Scotland, Slovenia, Sweden, Switzerland, USA, and Wales.
In 2015 the scientists Hofmann, Mätzler and Preuß determined the exact cause of the hair ice phenomenon, linking its formation to the presence of a specific fungus called Exidiopsis effusa.
They discovered that the presence of the fungus led to a process called 'ice segregation'. When water present in the wood freezes it creates a barrier that traps liquid between the ice and the pores of the wood. This creates a suction force that pushes the water out of the pores to the edge of the ice surface where it freezes and extends outwards. As this repeats it pushes a thin 'hair' of ice out of the wood which is around 0.01 mm in diameter.
It is believed that an inhibitor present in the fungus allows the strands of ice to stabilize allowing the formation of the beautiful phenomena and allows the hair ice to keep its shape often for several hours.
Exidiopsis effuse History
German scientist Alfred Wegener was the first to study hair ice. In 1918, he noticed a whitish cobwebby coating on the surface of hair-ice-bearing wood, which his assistant identified as fungus mycelium – the mass of thin threads from where mushrooms grow. He suggested there was a relation between the ice and the fungus in the wood.
Some 90 years later, Gerhart Wagner, a retired Swiss professor who has been researching hair ice for decades, found evidence of this relation: treating the wood with fungicide or dunking it in hot water suppressed the growth of hair ice.
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Photo 4 - Author: Rosser1954 (Creative Commons Attribution-Share Alike 4.0 International)