Icy hair (Exidiopsis effusa )
- Department: Basidiomycota (Basidiomycetes)
- Subdivision: Agaricomycotina (Agaricomycetes)
- Class: Agaricomycetes (Agaricomycetes)
- Subclass: Auriculariomycetidae
- Order: Auriculariales (Auriculariales)
- Family: Auriculariaceae (Auriculariaceae)
- Genus: Exidiopsis
- Species: Exidiopsis effusa (Icy hair)
- Ice wool
- Thelephora effusa
- Exidiopsis effusa
- Sebacina effusa
- Exidiopsis grisea var. effusa
- Exidiopsis quercina
- Sebacina quercina
- Sebacina peritricha
- Sebacina laccata
Hair ice, ice wool or frost beard, also known as hair ice, ice wool or frost beard, is a type of ice that forms on dead wood and looks like fine, silky hair.
This phenomenon is observed mainly in the Northern Hemisphere, between the 45th and 50th parallels, in deciduous forests. However, even above the 60th parallel, this amazingly beautiful ice can come across almost at every step, if there was only a suitable forest and the 'correct' weather (author's note).
'Icy hair' forms on damp, decaying wood (dead logs and twigs of various sizes) at temperatures just below freezing and fairly high humidity. They grow precisely on wood, not on the surface of the bark, and can appear in the same place for several years in a row. Each individual hair has a diameter of about 0.02 mm and can grow up to 20 cm long (although more modest specimens are more often found, up to 5 cm long). The hairs are very fragile, but nevertheless, they can curl in 'waves' and 'curls'. They are able to maintain their shape for many hours, or even days. This suggests that something is preventing ice recrystallization – the process of turning small ice crystals into large ones, which is normally very active at temperatures just below zero.
This amazing phenomenon was first described in 1918 by the German geophysicist and meteorologist, the creator of the theory of continental drift, Alfred Wegener. He suggested that some kind of mushroom might be the cause. In 2015, German and Swiss scientists proved that this fungus is Exidiopsis effusa, a member of the Auriculariaceae family. Exactly how the fungus causes ice to crystallize in this way is not entirely clear, but it is assumed that it produces some kind of recrystallization inhibitor, similar in its action to antifreeze proteins. In any case, this fungus was present in all wood samples on which 'ice hair' grew, and in half of the cases was the only species found, and its suppression by fungicides or exposure to high temperatures resulted in the 'ice hair' not appearing anymore.
The mushroom itself is rather inconspicuous, and if not for the bizarre hairs of ice, they would not have paid attention to it. However, in the warm season, they do not notice him.
Photo: Gulnara, maria_g, Wikipedia.