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Symbionts Survive

From the mostly-dead maple tree in our front yard, I've been peeling off bark, as it loosens, to lay it lichen-side up in the garden. I've gotten so fond of these bizarre gray--green frills, I just brought some into the house.

Other kinds of lichen can hang in festoons from trees, stick tight in thin layers to rocks, or raise miniature standing stems bearing spore capsules that look like fairy goblets or scarlet soldiers’ helmets....

These fantastic life forms are composed of two or three completely different organisms: one part fungus, one part algae ... or bacteria (or rarely, both). Taxonomy today classes fungi not in the plant kingdom, but in one of their own. Algae are plants; they conduct photosynthesis to manufacture carbohydrates, protein and vitamins ... but wait a minute, so do the bacteria (from another kingdom) that can partner with lichen fungi. In fact they used to be called “blue-green algae” but now the preferred designation is “cyanobacteria.” In most lichen however, it's regular green algae that photosynthesize, living inside the body of the fungus.

The fungus partner (mycobiont) absorbs moisture, and draws minerals from the surface it grows on — as well as from the dust in the air. Cyanobacteria photosynthesis also fixes nitrogen from the atmosphere. Lichen create soil from raw sand and rock. They also provide animal forage in marginal habitats (as well as traditional antibiotics and dyes).

Lichen are classified by the mycobiont, because there are thousands of varieties of fungi that lichenize, and none have been found living independent of a photosynthetic partner (photobiont). Only a few varieties of algae and cyanobacteria act as photobionts; they are often viable on their own, but having a tough fungal shell around them provides access to a much larger ecological niche.

Although polluted air kills lichen, they grow well — though always slowly — almost everywhere else, from Arctic tundra to rainforests to blazing desert, on almost any surface including manmade ones like roofing shingles, painted clapboard, concrete sidewalks, stained-glass windows ... even metal and plastic. Now we've learned they can survive in outer space.

Two species of lichen carried aloft by a Russian Soyuz rocket in May were exposed for nearly 15 days to vacuum and hard ultraviolet radiation. They went dormant, but back on Earth metabolism resumed, and scientists could find no damage — even to their DNA from the radiation.

The lichen I'm collecting could have come from some faraway galaxy.

Photo by C.H. Clark - Lichens I brought indoors, each about 1 inch across

Text and photos © Copyright 2005 Catherine Holmes Clark

Published in the six Nashoba Publications papers on Friday, 25 Novmber 2005

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