Lichens: mid-winter field observation · January 8, 2025

Though early January morning weather has been offering a wind chill factor of 0° F, it turns out that there have been good opportunities for field observation, prompted by my new lichen book.

The growth here is a hammered shield lichen, one of the most prevalent varieties globally and locally. It is a symbiotic combination of a fungus (Parmelia sulcata) and a green microalga (Trebouxia).

The microalga component has the capability of photosynthesis, deriving nutrient energy from the air and sunlight. It is notable here that the lichen displays a greenish tint even in mid-winter, in contrast to most of the deciduous plant life around it, now dead, brown and yellow.

The cells of the fungus are filamentary. As my reference notes, these threadlike structures weave into and around the alga, providing a firm base and skin. The durability of the composite is evident in the photograph. The lichen is still present and evidently alive, hanging loosely around the branch, long after the tree itself has died, the bark has dropped, and the wood itself is in marked decay.