Mosses and lichens

Lichens: More Complex Than Anyone Imagined

Lichens: so small, yet so complex! Photo:

Lichens are composite organisms often found growing on rocks and trees. Some species are commonly found in gardens, especially on well-established trees, and the advice to the home gardener has always been to ignore them: they’re harmless to plants and also add a bit of interest as well as (to a very minor degree) helping to fertilize the plants they settle on.

Lichens aren’t plants, though, but “composite organisms.” They were long thought to be simple combinations of one algae and one fungus. By joining their forces in symbiosis, each organism helping the other, the new composite organism develops properties different from those of its component organisms. 

Most algae, for example, cannot live outside an aquatic environment, but, sheltered within the cells of a fungus, they can now carry out their photosynthesis on a tree trunk, branch or rock. And the carbohydrates they produce feed the fungus … and some of the nitrogen they capture from the air drips down to the plant roots below. Everybody’s happy!

This symbiotic one algae/one fungi relationship has been known since the 1800s, but it turns out it’s more complicated than that. Scientists are finding lichens often have a third partner or a fourth or even a fifth!

There are often two fungi involved: an ascomycete fungus and a basidiomycete yeast. And in some cases, there is a second basidiomycete involved in the partnership. And other lichens have been found where there is one fungus and two algae species … and sometimes three. With some 17,000 identified lichen species in the world (and probably at least as many unidentified ones), the possibilities seem almost endless! 

I suppose symbiosis is rather like cooking: you need just the right ingredients to make things turn out!

Further Reading:

Not One, Not Two, But Three Fungi Present in Lichen

Symbiosis in Lichens

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

1 comment on “Lichens: More Complex Than Anyone Imagined

  1. Some clients believe that lichens are unhealthy to coast live oaks and apples because the unhealthy trees support so many of them. Actually, there are only more because the unhealthy trees do not exfoliate as efficiently as the healthy trees do. Lichens are an indication of distress.

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