Lichens & Mycorrhizae

by Michael Colebrook

The soil is teeming with life (1). I want to focus on just two elements of this life, both of which involve that that rather odd group of organisms, the Fungi. By tradition fungi are included in the botanical curriculum, although it is now believed that the group are more closely related to the animals than to the plants. The Fungi now have the status of a kingdom all to themselves.

Like animals, fungi need complex organic nutrients, and all fungi are saprophytic, (living off dead organic matter) or parasitic (living off living organic matter). The fungi involved in the two systems I want to describe have found ways of associating themselves with green (photosynthetic) organisms and by co-evolving have established mutually beneficial, symbiotic, arrangements with their green partners.

Historically there has been a marked reluctance on the part of evolutionary biologists to accept the existence of intimate, mutually beneficial relationships between different species. In evolutionary theory, competition rules, at least until recently. In his Analysis of Biological Populations (1972) Williamson stated ‘[mutualism] is a fascinating biological topic, but its importance in populations is generally small’ (2). This echoes Beatrix Potter’s dismissive reception by the Linnnean Society to her suggestion that Lichens exist as permanent associations between Algae and Fungi (3).

It is not altogether surprising that Beatrix Potter had a problem persuading the Linnean Society (and Kew Gardens) that lichens were symbionts. They are emergent entities and exist in forms that are sufficiently consistent to be classified as if they were individual species. It is estimated that there are about 20,000 different forms. The photosynthetic components, green algae or cyanobacteria, are capable of independent existence, the fungi are not, they are obligate symbionts.

Lichens on Rocks Cumbria UK.
Photo Dave & Lynne Slater
Lichen crust on tundra, Iceland
Photo Erwan Balança

Lichens play a vital pioneering role in soil formation. Thin surface crusts of lichens are found in most seemingly barren sites from deserts to arctic tundra. They form the first layer of organic matter and, where the conditions are suitable they provide the basis for the subsequent formation of soil. Lynn Margulis describes the process:Algae growing under the protective cover of fungi cling to sheer rock, extend over its face, and ultimately break it down into soil that can be penetrated by roots of plants and fungal hyphal networks. The hard rock of this spinning planet has been crumbling for hundreds of millions of years into rich, nutritive soil as a result of the fungal-algal partnerships.(4)

Without the Lichens there would be no soil. Without the soil there would be no complex life on land. We are most aware of Fungi in the form of mushrooms (edible) and toadstools (some edible, some not). But the real body of an individual soil fungus consists of long and very fine (microscopic) tubular cells, called hyphae, forming a more of less extensive branching and sometimes networking system known as a mycelium. These are not insignificant or transient entities, the mycelium of a specimen of Armillaria ostoyae (the honey mushroom) in a national forest in Oregon is believed to cover an area of nearly 9 sqkm (2,200 acres) and is estimated to be 2,400 years old! This is exceptional, the familiar fairy rings, which indicate the presence of an active mycelium underground, are usually only a few metres in diameter.

Some Fungi have developed symbiotic relationships with land plants known as mycorrhizae, literally fungusroot, which is a good name, it describes exactly what they are. The fungal element in the partnership merges with and extends the root system of the host plant. The host benefits from the extended root system. The very fine fungal hyphae can penetrate into smaller interstices in the soil than even the fine root hairs of the plant and they are very good at extracting nutrients, especially phosphates, from the soil. The fungus benefits by receiving a share in the energy rich, photosynthetic, materials made by the host.

There are two distinct forms of mycorrhizae. In Endomycorrhizae the hyphae penetrate the cell walls of the host plant but the cell membranes remain intact. The hyphae spread out into the surrounding soil for relatively short distances. The fungal species cannot exist independently. Here are about 130 species of endomycorrhizal fungi and all belong to the phylum Glomeromycota. The number of host species is not known but comprises a significant proportion of the total number of plant species.

In Ectomycorrhizae the hyphae form layers around the roots of the host plant and do not penetrate the cell walls. The hyphae radiate out into the surrounding soil for up to several meters.

The fungi are nearly all from the phylum Basidiomycota (toadstool forming). There are about 5,000 ectomycorrhizal species and they form alliances with about 2000 species, mostly conifers and nearly all are trees.

One of the ectomycorrhizal fungi is the quintessential toadstool, the Fly Agaric (Amanita muscaria). This produces the well known, bright red capped toadstool flecked with white which clearly signals that it is not one of the edible kinds. It also forms fairy rings thatmight encircle several trees. The single mycelium may be associated with several host trees. Most of the host and fungal species can exist independently but do not flourish nearly as well as when part of a symbiotic association. It is interesting to speculate on the marked difference in the numbers of species of endomycorrhizal (c 130) and ectomycorrhizal (c 5000) fungi.

Taxonomists place the endo- species in four orders, and all the members of these orders are exclusively mycorrhizal. It would seem likely that the habit evolved once only and the existing species are all descended from a common ancestor through differentiation involved in forming relationships with a enormous variety of host species. There is fossil evidence for the existence of endomycorrhizal species in the early Devonian period (c 400million years ago), long before the emergence of flowering plants.

The ectomycorrhizal species are found in three orders but the species involved are not all mycorrhizal. It is suggested that ectomycorrhizal species emerged together with the appearance of Conifers in the late Mesozoic (c 150 million years ago). The taxonomy would also suggest that the habit emerged more than once, through parallel evolution.

It is impossible to overestimate the significance of mycorrhizal associations for the flourishing of plant life of all forms and in all locations, they are a key element in the life of the soil. Along with Charles Darwin’s beloved earthworms, mycorrhizae are a vital part of the nearly invisible and often discounted infrastructure of life on Earth.


1. James Nardi. Life in the Soil (University of Chicago Press, 2007).

2.MarkWilliamson. The Analysis of Biological Populations (Academic Press, 1972).

3. Michael Colebrook. ‘What have Lichens to do with Peter Rabbit’ (GreenSpirit, Summer 2002), p. 7

4. Lynn Margulis. The Symbiotic Planet (Weidenfeld & Nicolson,1998) p. 109.

Michael Allen. The Ecology of Mycorrhizae (Cambridge University Press, 1991

A classification of the whole Kingdom can be found at:

The Dirt Beneath Our Feet

by Marian Van Eyk McCain

Adapted from her book Elderwoman: Reap the wisdom, feel the power, embrace the joy (Findhorn Press, 2002).

Like many older women, then and now, my grandmother was a keen gardener. When I was five, she donated a little patch of her garden to me, and gave me sunflower seeds to plant. For ages, nothing happened. Then, tiny shoots appeared. 1 watched in amazement as the plants grew and grew until they were more than twice as tall as me, their huge yellow heads nodding over, way above my head. It seemed like a miracle. Well, it was, really.

Back then, I assumed that soil was just inert stuff that held the roots and supported the plant stems. No one told me otherwise. It was many years before I really understood what an amazing and important substance soil is, and how unappreciated and badly treated it is by some sections of humanity. Yet a good relationship with it can enrich our lives, which is why I want to begin this essay by thinking about the soil very literally.

Dirt, soil, earth. The topsoil, the subsoil, the rock underneath.  All our lives, we rest upon it. Depend upon it, literally, in all senses of the word. Yet If you think about it, we modern folk spend very little time with our feet actually touching the earth itself. Some of us might go a whole day without glimpsing bare soil. We can even forget that it exists. Much of the time, especially if we live in the city, between that soil and our feet lies the dead weight of concrete, sitting dully and heavily over soil which may never see the sun again. That always makes me feel sad. Although I know it is a silly fantasy, since builders always remove the topsoil before they build, I still have this image of some poor mole or earthworm struggling to the surface only to discover he or she has come up right under the middle of Safeway or the Interstate or Gate Fifteen of the airport. It is a dilemma, for I need stores and roads and airports, too, just like everybody else does.

I also need the soil, for my life utterly depends upon it. Without soil, there would be no food, and without food we would all die. So it seems important to me to think about this dirt, this thing that one’s life depends on.

Firstly, I believe we need to think about it in order to ensure that it is being properly taken care of and that there is enough of it that is not covered over. Lots of areas where the trees can grow and the moles and earthworms can still poke through the surface.  And lots of it that never will be covered over – ever. Because land developers and builders – and governments – often don’t notice when they are overdoing things and putting profit ahead of health and sanity. Sometimes it needs older people like me to point this out; people who have been around a long time and who can see the long-term effects of things are the ones who need to speak out. Just as longitudinal studies in science are a particularly useful and valid way of gaining information, the voices and opinions of older people in a society have a value all their own. It is we who remember the green field which predated a certain parking lot, cattle grazing in what is now the shopping mall, the chopped-down trees. That’s when we find ourselves crying out “STOP!” for we truly understand what is being lost.

Secondly, I think we need to look at our relationship with the soil from the point of view of having been created out of it, and being headed towards intimate reunion with it after our death. Realizing the importance of that relationship, we might want to put more emphasis on celebrating that deep connection. We might want to find opportunities in our lives to walk barefoot, to dig in the garden, plant things in the soil, smell it, get it on our hands. There is literally an earthy satisfaction for many of us in those things, a satisfaction which we may have forgotten in our busy lives up among the concrete buildings, and which will come flooding back when we walk barefoot along the beach or spend an afternoon on our knees in the garden, weeding and planting and mulching.

Thirdly, it seems important to consider the symbolic aspect of it. In other words, the necessity to stay grounded. Physically, we do this by remaining aware of our bodies and not ignoring or overriding their messages of weariness or pain. Emotionally, we do it by keeping a firm hold on reality and commonsense and by tempering drama with humor. And spiritually, we do it by honoring where we come from, our emergence from the ‘stuff’ of the Earth.

So, if the bodies we live in are actually constructed out of the earth, and earth is the substance on which our life and existence depends, surely it must be a highly important substance? Something to give some thought to. What actually is it? Why does it do often get treated as dispensable, as insignificant–or even as horrible? (‘Dirt’ –  ‘dirty ’–  ‘disgusting’ )

I remember thinking about that one day, many years ago, after I had been standing in an airport departure lounge, watching a grandson – then not quite a year old – toddling around on the floor, trying out this new mode of locomotion so lately learned. I recall the way his curved, pink baby feet struggled to splay flat and hold his body vertical. He stepped, he wobbled, he collapsed. Tried again, collapsed, gave up, returned to crawling mode. This he could do, of course, with the speed of several months intensive practice. So off he went, skimming across the vast acres of polished airport vinyl, dodging the travelers and their suitcases. He reached a large trash can of cylindrical metal, twice his height. Up went the hands, fingers seeking, exploring. On to his feet again then, stretching up, those little fingers curling over the top of the trash can, gripping, pulling, until down it came, in a shower of cigarette ash, apple cores, Styrofoam cups and candy wrappers. He settled down contentedly, amid his booty, keen to examine every new object, perhaps to taste some.

By the time I retrieved him, his pink hands and feet and knees were a grimy gray and I tucked him on to my hip and raced for the washroom as though the seeds of a dozen weird and possibly fatal diseases were waiting only for him to put a finger in his mouth.

As I held him firmly with one arm around his waist and used my free hand to wash those baby fingers, my mind went back one week. We had been in the country, staying in our small cabin.

There he was, in my memory’s eye, crawling to the edge of the cabin doorway and easing himself gently over the step. There he was, crawling across the uneven brick paving, pausing to examine and to taste the weeds that grew between the cracks, to pick up a small stone, to dabble in the untidy place where paving and grass met, their boundary blurred by the sprawl of alyssum and nasturtiums.

Off he scuttled, emboldened by a quick look behind him to check that his mother and I were still waiting and caring; off to the mysteries of rainwater tank and bucket, of rock and log, of soft leaves and prickly leaves, darting skinks and slow-moving beetles, and above all, of earth. Dark brown earth.

I remember him coming back, his knees now green from grass, fragments of soil and sand in the soft crevices of his plump little hands, and I remember how I scooped him up and fed him some mashed carrots on a spoon and then, after a while, returned him to his mother’s breast for milk and sleep, and none of us even thought of washing him. So what was the difference? He was dirty, but this time it didn’t matter. Why not?

What, then, is dirt? Words like ‘dirty’ and ‘soiled’ seem to denote some unhealthy, unpleasant state of being, a contamination. But it was only after the airport incident that the truth came to me. The truth that there must once have been a time when the only way you got dirty was in the dirt. The only way you got soiled was in the soil. There was no other class of dirt except that which lay on the forest floor of our ancestors, or within the caves they used for shelter.

The soil, then as now, was made up of three basic types of ingredients: minerals (the fragmentary particles of all kinds of rocks), humus and living organisms. The humus was composed of a vast conglomeration of once-living matter, the waste products of creatures, the broken down remnants of plant parts, all combined into a rich, nurturing compound, essential to continuing life. It was from this compound that seedlings drew their nourishment and built themselves into grass, flowers, trees – green and growing things which, in their turn, nourished and built the animals. Organisms living within this soil mixture – molds, bacteria, worms and other creatures—made up the huge army of workers that converted the raw materials, like dead plant and animal matter, human and animal wastes, etc., into usable form. A huge army which, by the way, is still largely unstudied. It is an astounding fact that only a mere 5 percent of soil organisms have ever been described and classified even though there are thousands of different kinds in every teaspoonful of soil. I always used to assume that scientists knew everything there was to know about soil, but apparently their knowledge is extremely limited.

Once all these decaying and putrefying materials are fully decomposed and turned into humus, they are sweet smelling, clean, beautiful and wholesome again. They eventually become the crumbly chocolate-colored compost into which we love to plant our daffodil bulbs.

But between the decaying, rotting matter and the sweet smelling compost there is a time gap—and, for most of us, an awareness gap. The process of transformation is slow and mysterious and takes place mostly in the dark. So we see the two ends of the cycle but not the middle. Unless we recycle everything ourselves. Then we see the whole cycle. But most of us throw our garbage in the bin and we buy the compost at the garden store and we rarely if ever think about what lies between these two events.

When I rushed my grandson to the airport washroom, the dirt on his little pink hands seemed menacing somehow, ugly, out of place, obscene. It seemed to contain the dirt of a thousand feet that had walked who knows where, over who knows what. The noxious mixture from the trash can was the raw detritus of a culture that no longer recognizes the existence of its own waste products, let alone honors and recycles them. And many are not recyclable anyway. Therefore, this unknown mixture on his innocent hands repulsed and terrified me at some unconscious level where I intuitively felt –  rather than thought about – the difference.

Around that cabin, on the other hand, things lived and things died, and everything, even peoples’ own waste products, ended up eventually as sweet smelling compost in the garden or the orchard. (The residue from the composting toilets, by the way, only goes into the orchard, and not on the vegetable patch.) The process may be mysterious and wonderful, but the processed components are known. We always knew what went in, and always knew what came out. Daily, we remembered to bless the seen and unseen army of converters, the earthworms and their zillions of smaller companions that thrive beneath the surface of our soil. The child, crawling there, was crawling in the known world. Lightly guarded by those who know which berries and which spiders to watch out for, he was safe in his adventuresome exploration of the earth.

So I think that quality of familiarity with the earth, with the movement of things in and out of it, is something we have largely lost. Our loss of that familiarity and knowing, and the pollution of the soil by umpteen industrial and commercial processes that we know so little of, has separated us from that which is really the matrix of our existence. It has made us strangers to the soil and made of dirt a foreign and potentially lethal substance. In a way, we have become strangers to ourselves – to our own bodies and to their matrix.

The soil, and the rock below it, is the body of the Earth. The body with which we were born and in which we age is our borrowed piece of soil. We leave it behind us when we die, returning it to whence it came. So to me it makes sense that while it is in our care, we take good care of it. Like a library book, we should not trash it. Similarly, it behooves us to take good care of the Earth’s body too, since everything else which lives depends on that. To me, there is a deep connection between the way we take care of our bodies and the way we take care of the soil and of the world. Start thinking about one, follow it far enough and it inevitably leads you to thoughts of the other two. Want to be more healthy? Improve your diet. Which means eat better quality, cleaner food – organic food. Which means healthier soil. Which means a healthier planet. Our bodies are the soil, they are the Earth. As the Irish philosopher John O’Donohue so lyrically expressed it in his book Anam Cara, we are beings made of clay.

‘We so easily forget that our clay has a memory that preceded our minds, a life of its own before it took its present form. Regardless of how modern we seem, we still remain ancient, sisters and brothers of the one clay… The human body is at home on the earth.’

So when my own grandchildren planted sunflowers in my garden, I had a lot more to tell them than my grandmother had told me. About the importance of soil, and the creatures who live in it. About the importance of nurturing and protecting it, for all our human sakes and for the sakes of all those non-human life forms with whom we share the planet. About its sacred nature. They needed to learn about humus. And about the huge, unthanked workforce of indefatigable beings who create the basis for new life out of the raw materials of death. A healthy patch of soil, I told them, is a huge, complex ecosystem in itself. An underground community. A vast co-operative project undertaken by billions and billions of tiny interdependent creatures, most of whom we neither see nor know the names of. All of them matter

I hope the children listened. So when that grandson who pulled over the trashcan now walks through the airport wheeling his suitcase, I hope he remembers the soil beneath the concrete and the creatures of the earth. I hope they will still be there for him, in even greater numbers, as people gradually begin to remember the importance of soil, of dirt, of earth. And I hope there are many days in his man’s life when that soil is sweet upon his hands and rich beneath his fingernails.