In 1867, Simon Schwendener startled the scientific world when he announced to the Swiss Naturalists’ Club that lichens were not the distinct organism they had long been thought to be, but rather were formed of two separate organisms: a fungus and an alga. Leading lichenologists were outraged at the radical idea; not for 50 years would Schwendener’s theory be accepted. But once it was, lichens were seen as a classic example of a mutually-beneficial symbiosis: The alga, able to photosynthesize, provides food for the fungus; the fungus provides shelter and water to the alga.
Some 20,000 kinds of this unique association grow on earth, living in almost every environment, from within Antarctic rocks to the surface of desert soils. Lichens can withstand years of desiccation by simply becoming dormant. They revive again with miniscule amounts of water – in the desert, humid night air suffices. While dormant, lichens can also stand searing heat and extreme cold; some species can survive temperatures as high as 180ºF and as low as 100ºF below freezing. Some arctic lichens are estimated to be over 4,000 years old, among the world’s oldest plants.
What looked to early botanists like a single plant is actually a highly-organized association of hundreds to millions of microscopic algal cells woven into a fabric composed of fungal filaments, or hyphae. The fungus forms the thallus, or body of the lichen; the algae, arranged in a thin layer near the top of the thallus, absorb solar energy and produce food.
{ 0 comments }
