Contributed by Joy Window, Member, Big Scrub Landcare.

When you walk through a rainforest, your attention is probably grabbed by the majestic trees and the sounds of birds, tumbling streams or the wind. But if you look down at your feet, you’ll find another equally fascinating world – that of fungi and slime moulds. What we think of as mushrooms are technically called the ‘fruiting bodies’ of a fungus. The main part of the fungus is a spaghetti-like net called the mycelium, which spreads over the ground or fallen tree or into the soil of the rainforest.

The mycelium is often microscopic but you can sometimes see it. Fungi can be divided into three categories: saprophytic, mycorrhizal and parasitic. Saprophytes (the main ones in rainforest) rot down dead material, allowing minerals to be recycled into the soil for use by living trees and other organisms. If they didn’t exist, what rainforest was left would be sky-high in fallen branches and trees.

The mycorrhizals have a ‘mutualistic’ association with living trees – the fine web of the mycelium gets into places tree roots can’t and extracts water and minerals, passing them into the tree roots. The tree in turn supplies the mycelium with the sugars it needs for life. All eucalypts and pines rely on this source of energy.

The parasites live on plants, insects, and animals, causing disease in agricultural crops, for instance. You might have heard of the cordyceps fungus that takes over some ants, changing their behaviour so that they walk out away from shelter where the fungus breaks through their skin, killing them, in order to distribute its spores into the open air. Fungi even grow on us humans, causing tinea, ringworm and lung diseases.

Birds, insects, worms, bacteria and mammals like the long-nosed potoroo of the North Coast eat fungi and help distribute the spores.

Another weird wonder of the forest floor is the slime mould. It’s not a plant, a fungus or an animal, although it can move like an animal. One of the most visible of the slime moulds is Fuligo septica, also known as dog’s vomit or caca de luna (moon poo). While looking like a slowly moving clump of scrambled eggs, it is actually one giant cell. It moves about the soil, feeding on bacteria, fungi and algae. When it’s ready, it stops moving and produces tiny (1.5–3 mm tall) stalked fruiting bodies, which produce dust-like spores. The spores form small, single cells which eventually merge to form the plasmodium stage (the dog’s vomit), which is the stage that moves, and the cycle continues. Springtails, beetles, snails (especially the Giant Panda Snail of the Big Scrub rainforests), slugs and flies eat slime moulds and help spread them.

So don’t forget to look down when you walk through the rainforest after a rainy day. Look at fallen tree branches and the inner surface of bark. Don’t forget to put everything back exactly as you found it – some fungi (and other organisms that live in the same places) can’t cope with drying out. It’s a different world!