Fungi are a very common and diverse group of organisms that includes mushrooms and puffballs, yeasts and moulds. They are found everywhere – in all habitats on land, and also in fresh water and the ocean. They were once grouped in the plant kingdom, but unlike plants they cannot make their own food through photosynthesis, and they digest their food externally before absorbing nutrients
There is no clear distinction between mushrooms and toadstools. Toadstool is a common but vague term for some kinds of mushroom, usually a poisonous or inedible one. Toads were once thought to be very poisonous, but ‘toadstool’ is said to come from the German tod-stuhl, meaning death-chair – referring to the the fatal effects of mushroom poisoning, and to the shape of the fruiting body.
Fungi are more closely related to animals than to plants – for example, they are mainly composed of chitin, which forms the exoskeleton (covering) of insects and other arthropods. However, they are now considered distinct enough to warrant their own major grouping – the fungi kingdom.
When asked to name some fungi, people usually think of mushrooms, toadstools and puffballs. But these are just the reproductive parts of certain types of fungi. Most fungi lie underground or in wood or leaves as a spreading network of fine tube-like filaments called hyphae. As the fungus grows, these branch and interweave, seeking nutrients for growth. Eventually they form a cobwebby mat known as a mycelium. This is the body of the fungus.
Some fungi are microscopic and single-celled (for example, yeasts). At the other extreme, a North American relative of New Zealand’s bootlace mushroom Armillaria novaezelandiae is reported to be among the largest and perhaps most ancient organisms in the world, with an underground mycelium spreading over hundreds of hectares.
Fungi do not have chlorophyll and so cannot make their own food by photosynthesis. Instead, they gain nutrients from living or dead material around them, including soil and wood. There are five fungal groups, each with a specific survival strategy:
Most fungi reproduce by spores. These are simple structures, usually a single cell with a protective coating. Each spore is microscopic, and as a mass they look like dust or powder.
A fungus produces vast numbers of spores, which are spread in various ways – for instance by wind, raindrops or animals. When a spore falls in a suitable site it germinates into a hypha – the first of the threads that make up the body of a fungus.
In terms of species, fungi far outnumber plants. Worldwide there are an estimated 1.5 million species of fungi (compared to 250,000–420,000 flowering plants). By 2004, about 7,500 species of fungi had been recorded in New Zealand. However, this is not a true reflection of the country’s fungal diversity, because many groups of fungi have not been well studied. The actual number of species is thought to be around 22,000. Over 900 species have been recorded growing with the four species of native beech.
Like all forms of life, fungi can be threatened by habitat loss and other effects of human activity. Among New Zealand’s most endangered organisms are 49 species of fungi, including:
Where a fungus grows only on a plant species that is itself threatened, it may be more endangered than its host.
Some New Zealand fungi are edible, while others are unpalatable or poisonous. A few are deadly poisonous and can be easily confused with edible ones. There is no general rule to distinguish them, and tasting is never recommended when searching for edible fungi. Correct identification is essential.
Puffballs are a familiar type of fungus in New Zealand. Their Māori name is pukurau, and in earlier times, Māori cooked and ate them when fresh, and applied the spores to burns. The town of Waipukurau, in Hawke’s Bay, takes its name from the fungus.
A few native and introduced mushrooms (Psilocybe species) can cause hallucinations if eaten. Known as magic mushrooms, these small, brown species are difficult to identify, and illegal to harvest.
The New Zealand Fungal Herbarium at Landcare Research, Auckland, is the centre for scientific research on New Zealand’s fungi. It has around 80,000 dried specimens from around the world. A further 7,000 living strains of fungi are held in the adjoining national culture collection. Fungal scientists (mycologists) do research on native fungi, and on introduced fungi that pose a biosecurity risk because they cause plant diseases.
Saprobes are the group of fungi that act as decomposers, feeding on dead and decaying wood, leaves, litter, and other organic matter. To digest this they secrete enzymes that break it down. This releases and recycles vital nutrients for other organisms, and helps dispose of organic waste. Decomposers are essential for the survival of ecosystems.
Saprobes are the most common type of fungi. Many are too small to see with the naked eye. However, the saprobe group includes New Zealand’s best-known fungi with large fruiting structures (mushrooms), including most cultivated edible mushrooms.
Sapstain fungi produce a dark stain inside the wood they grow on, which reduces the commercial value of timber. But native wood that is stained blue-green by native cup fungi is valued for crafting into finely inlaid woodware.
Many saprobes produce stalked mushrooms that fruit on soil and wood. They include the introduced ink caps (e.g. Coprinus comatus) and field mushrooms (Agaricus campestris) on grass, and ‘big gyms’ (Gymnopilus junonius) on stumps and wood. In these species, the spores form on gills beneath an umbrella-shaped cap.
Polypore fungi produce spores from the inner surface of tiny tubes, under a structure that juts out like a shelf or bracket. Examples include large bracket fungi (Ganoderma species) and the annual rainbow bracket (Trametes versicolor).
The bright-orange pore fungus Favolaschia calocera is a mushroom, but with shallow pores on its underside. This introduced species was first reported in New Zealand in the late 1960s. It has weed status in many native forests, where it grows on a wide variety of wood.
Other saprobic fungi develop spores on smooth outer surfaces (e.g. Aleurodiscus berggrenii, a crust fungus), on coral-shaped branches (e.g. Clavicorona pyxidata, a coral fungus) or within cup-shaped structures (e.g. Aleuria rhenana, a cup fungus). In most of these the spores are dispersed on the wind.
The stinkhorns, such as the red flower fungus Anthurus archeri, use insects to spread spores by attracting them to a sticky and stinking spore mass. They are common on wood chip mulch in gardens, and you are likely to smell their rotting-flesh odour before you see them.
Another commonly seen group of fungi are the sooty moulds, which form black carpets over the trunks and branches of beech trees. To get nutrients, sooty moulds break down sugars in honeydew excreted by scale insects that suck tree sap – the same honeydew taken by native birds and invasive wasps.
Harore, the native bootlace mushroom, was widely eaten by Māori. Its English name refers to the thick ribbons that weave along plant roots and through soil to find food. While it usually breaks down dead logs and roots, the mushroom can live as a parasite on crop plants such as kiwifruit and radiata pine. Freshly decayed wood taken over by this fungus may emit a weak light (known as bioluminescence).
Māori traditionally used several saprobic fungi as food, including the toothed pekepekekiore (Hericium coralloides) and basket fungus or kōpurawhetū (Ileodictyon cibarium). Puffballs such as pukurau (Calvatia gigantea) were also used to staunch bleeding, and as anaesthetics. The wood ear or hakeka (Auricularia cornea) was both eaten and traded. In the late 19th and early 20th centuries huge quantities of this fungus were collected and dried by Māori, for export to China. This trade in ‘Taranaki wool’, as it was known, was managed by Chew Chong, who was recognised for his contributions to the dairy and fungus industries.
Mycorrhizal fungi have a close and beneficial association with the roots of plants. Most plants co-exist with these fungi, which help them absorb nutrients from the surrounding soil.
The body of a fungus consists of many hyphae (fine threads or filaments). In mycorrhizal fungi these extend from the host plant’s roots into the soil, greatly increasing the surface area for the absorption of nutrients by both the fungus and the plant. In return the fungus, which cannot make food from photosynthesis as plants do, receives carbohydrates produced by the plant’s leaves.
There are two main groups of mycorrhizal fungi: ectomycorrhizal and endomycorrhizal.
The hyphae of these fungi form a covering around the root tips of host trees, grow between the cells of the root cortex, and cause the root tips to become branched. They usually co-exist with one or only a few plant species.
Several hundred New Zealand ectomycorrhizal species are endemic (they are found nowhere else). They are most obvious in autumn, when they send up mushrooms under trees. Cortinarius elaiochrous, for example, grows with beech (Nothofagus species), and Amanita nothofagi with beech, mānuka and kānuka (Leptospermum and Kunzea species).
Other ectomycorrhizal fungi include:
Introduced ectomycorrhizal species, though less varied, are common under exotic trees such as oaks and pines. They include fly agaric (Amanita muscaria) and pine bolete (Suillus granulatus). Fly agaric has recently been found growing under native beech trees, where, as an invasive species, it may be competing with native fungi.
Endomycorrhizal fungi live on a wide range of host trees and other plants. Unlike ectomycorrhizas they do not form large, visible fruiting bodies. Instead, their hyphae form a closely woven cover around plant roots, and nutrients are exchanged through fine branches (arbuscules) that push into plant cells without breaking the cell membrane. They are mostly only visible to the naked eye as packets of spores (often yellow) among soil particles.
Truffles, an expensive fungal delicacy, grow underground and are sniffed out by trained dogs. The introduced black truffle Tuber melanosporum is now cultivated in New Zealand as an ectomycorrhizal associate on the roots of oak and hazel trees. The native truffle-like fungi are small and sometimes colourful. They mostly live on the roots of beech or mānuka/kānuka trees, and are probably spread when animals such as ground-feeding birds eat them.
Another kind of fungus–plant association exists with non-photosynthetic orchids. In New Zealand one example is a three-way relationship involving harore (the native bootlace mushroom), the parasitic orchid Gastrodia cunninghamii, and beech trees. Harore acts as a go-between, passing sugars from the host beech tree to the orchid, which cannot produce food by photosynthesis. In this case the orchid is acting as a parasite of the fungus.
Parasitic fungi feed on living plants and animals, and are the main cause of plant disease worldwide.
Most diseases of pasture grasses and crops for horticulture, agriculture, and forestry are caused by introduced fungal parasites. Practices such as spraying fungicides are needed to minimise the damage.
Most parasitic fungi are microscopic and may be better known by their symptoms (such as brown rot in peaches). Domesticated animals are also harmed by toxic introduced fungi – for example Pithomyces chartarum causes facial eczema in cattle and sheep. Another non-native fungus, the chytrid Batrachochytrium dendrobatidis, has been implicated in the global decline of frogs, including the rare Archey’s frog in New Zealand.
A variety of fungi have been collected from human nail infections, and several can infect people who are weakened, for example by damaged skin or an impaired immune system.
Although there are several native parasitic fungi, their impact on native plants and animals is largely in balance as they have co-existed for millions of years.
The fungus known as beech strawberry (Cyttaria species) causes cancerous galls on beech trees. In spring, these develop into yellow, golfball-like fruiting bodies. They are eaten by pigeons and possums, and in South America related species are harvested for human consumption.
The native pūtawa (Laetiporus portentosus) causes wood decay in living silver beech. It forms large, bracket-shaped fruiting bodies that were harvested by Māori for use in fire-starting and fire-carrying, because they smouldered for hours. There are several native fungi parasitic on leaves. For example, Corynelia tropica causes spots on the leaves of tōtara trees.
Vegetable caterpillar (Cordyceps robertsii) was the first new fungus described in New Zealand, in 1836. It is a parasite of the ground-dwelling caterpillar stage of certain native moths. The fungus mummifies the caterpillar, then forms a stick-like fruiting body from the caterpillar’s head, extending up to 20 centimetres above the ground. Māori burned the fungus (known as āwheto) to make powdered charcoal as a black pigment for tattoos. They also considered it a delicacy.
A few native fungi have become parasitic on introduced crops. Harore, the bootlace mushroom (Armillaria novaezelandiae), usually decomposes dead logs and roots, but it can become parasitic on crop plants such as radiata pine and kiwifruit if it is already present in the soil where they are planted. This readily occurs where native forested land has been converted into forest plantations, and in kiwifruit orchards where willow shelter belts are felled – their stumps and root systems become infected by the mushroom. It then spreads to nearby living roots of kiwifruit and becomes parasitic on the plant.
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