There are so many amazing facets of nature that tend to slip by unnoticed. Think about the last time you walked in the woods. Where was your attention? Did you think about the trees, the landscape? Or maybe the organisms you either could see and hear or that you imagined might be nearby? Did your gaze ever pause on the rocks or tree trunks encrusted with the inconspicuous forms of lichens?
When you do notice lichens, their difficult, astonishing existence becomes apparent. Lichens occur in the most inhospitable places: on trees, rocks, and roof shingles; in extremely cold environments like the Arctic and Antarctic; and even as crusts on top of desert soil. How is it that this organism–is it a plant? A fungus?–can survive where so many others cannot?
Jane Hirschfield’s poem, “For the Lichens,” is a journey of awareness. The speaker knows about the trappings of cities, but the discovery of lichen opens up a world she hadn’t known existed:
Back then, what did I know?
The names of subway lines, buses.
How long it took to walk twenty blocks.
Uptown and downtown.
Not north, not south, not you.
When I saw you, later, seaweed reefed in the air,
you were gray-green, incomprehensible, old.
What you clung to, hung from: old.
Trees looking half dead, stones.
Hirschfield hints at the answer to one of our questions when she calls lichen “seaweed reefed in air.” As it turns out, lichen is often both a plant and a fungus; it is a stable association between a fungal body and a photobiont, that is, a symbiotic partner capable of photosynthesis. Most commonly, the photobiont is an alga, but sometimes that role is filled by cyanobacteria, an ancient form of photosynthesizing bacteria.
Symbiosis, in biology, is an interaction between two organisms that is beneficial to both. When the photobiont in the partnership is algae, the fungal body protects the alga, and the alga provides food through the process of photosynthesis. When, instead, the partner is cyanobacteria, it performs photosynthesis and also nitrogen fixation, taking nitrogen from the air and making it available to the fungus. These interactions greatly increase the range of both organisms, allowing them to survive in environments that neither could handle alone.
Marriage of fungi and algae,
chemists of air,
changers of nitrogen-unusable into nitrogen-usable.
Like those nameless ones
who kept painting, shaping, engraving
unseen, unread, unremembered.
Not caring if they were no good, if they were past it.
Reproduction in lichens can be as complicated as you might imagine for a body composed of two symbiotic organisms. Certain lichens can reproduce asexually, either vegetatively through broken-off pieces or with structures called soredia, little bundles of algal cells surrounded by fungal threads. A few kinds of lichen can reproduce sexually, though it should be noted that only the fungal body is actually reproducing in these cases; after germination, a suitable photobiont must be found to form a lichen. In sexual reproduction, two different kinds of spores are produced (they can be loosely thought of as “male” and “female”), which meet and combine genetic material.
The body of a lichen, called the thallus, is a combination of algal and fungal cells. General body form, determined largely by the fungus, fits into one of three classifications: crustose lichen occurs as a crust on a surface, often rocks; foliose lichen appears leafy and lobed; and fruiticose lichen has upright, branchlike structures. The final stanza of Hirschfield’s poem begins by listing images inspired by lichens:
Rock wools, water fans, earth scale, mouse ears, dust,
Transformers unvalued, uncounted.
Cell by cell, word by word, making a world they could live in.
What an incredible feat, to change the environment to make it more suitable for yourself! What organism, besides humans, can manipulate its world to such a dramatic extent? And yet, this complex interaction of fungus and algae is occurring all the time in a nondescript little package. So the next time you’re outside, look a little closer at your surroundings. Try to remember the intricacy of what is all around you, worlds within worlds.
“For the Lichens” by Jane Hirschfield, published online by The Atlantic. Read it here.
“Lichen Biology” University of Sydney’s School of Biological Sciences Online Learning Resource. Link.
“Lichen” 15 October 2008. HowStuffWorks.com. Link.