Mushrooms
The Shroom Life Cycle

What little fossil evidence there is suggest that fungi per se have inhabited the earth for at least 400 million years, since the Devonian period.  It has been estimated that there are as many as 1.5 million species of fungi currently in the world, of which only about100,000 have been identified and formally described, with most being found in the tropics.  – the fungi actually constitute a distinct biological kingdom, for they contain no chlorophyll and do not reproduce with flowers.  But of the four major fungal phyla, in which may be found the rusts, smuts, yeasts, moulds and mildews, only the so-called Basidiomycetes produce what we commonly think of as mushrooms and toadstools.  There may be as many as 140,000 of these mushroom-producing species in the world, of which we may know only as few as 10 per cent.

Mushrooms  - or carpophores, to give them their scientific name do not represent the entirety of the organism, merely the reproductive structure, or fruiting body concerned with propagating genes into the next generation.  The main body actually consists of network of microscopic threads, or hyphae, which grow and branch through the species’ preferred substrate, forming what is called a mycelium.  Mycelia can grow to a vast size. One of the largest has been found in America, a single root fungus, and Armillaria bulbosa.  This specimen occupies an area of about fifteen hectares, weighs in the region of 10,000 kg, and is probably about fifteen hundred years old.

Mushrooms and toadstools exist solely to produce spores, which they do by the million.  Released and sometimes fired forcibly into the air, these microscopic “seeds” are blown away by the slightest breeze until, if lucky, they land on a suitable substrate where, when conditions are right, they will germinate.  A single hyphal thread hatches out of the spore and expands outwards, rather like the long modeling balloons used by stage conjurors, but inflated by water pressure, not air.  The hypha grows, splits and branches this way and that, sensing its way to where pockets of nutrients can be found and absorbed through its semi-permeable wall.  At this stage the fungus is monokayotic, that is, it contains only one nucleus and one complete set of chromosomes and though viable for a short time, will die if it does not “mate”.  Unlike the dioecious higher organisms, fungi have many hundreds of different mating types – sexes if you will, though the analogy is not precise - to choose from.  When two compatible types meet, they fuse together in such a way that each hyphal cell then contains two distinct nuclei, two complete sets of chromosomes, which coexist together harmoniously until environmental cues trigger true sexual reproduction. 

In the temperate zones fungal reproduction is usually spurred on by the onset of winter – frost being the greatest enemy of an organism consisting mostly of water – but elsewhere shortage of nutrients may be the trigger.  When environmental cues indicate a period of stress, the ever expanding hyphae suddenly grow together into tight balls, called pinheads Then, from these, and occasionally rising with such force that they can dislodge paving slabs, mushrooms grow up and out, an architectural triumph to rival the finest humans can offer.  

It is only here, within the cells of the mushroom itself, that true sexual reproduction occurs.  The two nuclei fuse, meiosis takes place, and spores are formed, which then drop away from the mushroom’s gills or pores, caught by the breeze and blown far and wide.  But with their tough coats spores can lie dormant for years, weathering the harshest of conditions. For such a fragile organism, spores are an eminently sensible way of ensuring that those selfish fungal genes are passed on.

The majority of fungi, whether mushroom-producing or not, are saprophytic, that is they are nature’s recycles, feeding off dead plant and animal cells.  However some are symbiotic, bonding with algae to form lichens, or together with plant roots to form complex underground networks called micorrhizae, a “wood-wide web” without which both plants and fungus would struggle to survive.  Others are parasitic

© Shroom Liberation Front 2007