Microfungi

A large, beautiful and diverse group, micro-fungi remain a mystery to almost everyone except mycologists and plant pathologists.

In contrast to macro-fungi, most of which are easily visible, micro-fungi can only be studied properly with the aid of a microscope, however, what they lack in size they make up for in more widespread distribution, primarily because it takes less moisture for them to produce their fruiting structures.

Micro-fungi come in incredibly diverse, fascinating and complex shapes, and when examined microscopically are shaped very differently to the macro-fungi. People who are knowledgeable about both of these groups are rare indeed.

Aspergillus species also produce chains of spores with milk bottle-shaped cells.

A species of Penicillium. Note the chains of spores formed by milk bottle-shaped cells.

Septosporium sp.

Aurapex Penicillata (about 2 to 3 mm high) occurs on the bark of Tibouchina species in Colombia.

A lengthwise section through a species of Pleospora showing the spores formed inside.

When you’re looking at mildew, bread mould, the little black dots in the dead spots on leaves, the little hairs or bumps on dead wood, the green, white or blue powdery fluff when you turn over moist, rotting wood, or the green fluff on rotting oranges, you are looking at micro-fungi.

Similarly, the blue or green lines in some cheeses (mostly the ‘aromatic’ ones…) are a fungus growing and fruiting inside the cheese. All these fruiting bodies are conspicuous once you know what to look for, but are too small to see in any detail without some magnifying aid. Other micro-fungi are so inconspicuous that to find and view them one needs experience, special methods and sometimes even blind faith!

As with the macrofungi, the two main groups also apply to the microfungi and you thus get Ascomycetes and Basidiomycetes. There is also a third group: Zygomycetes, into which fungi like common bread are classified. Within all of these groups some of the individual fungus types may take on two forms: one being the fungal equivalent of a plant’s flowers, which need sexual recombination, while the other form makes fruiting bodies that produce spores asexually. Like plant cuttings, these spores will give rise to new fungal colonies that are exactly the same as the parent. The two forms often look different from each other, but are the same fungus.

Although microfungi produce their spores in various ways, a rough division separates them into two groups: those that form their spores inside specialised structures, and those that simply generate spores from within their regular cells. Whether or not specialised structures are utilised, there are various adaptations to ensure that the spores are distributed. Some fungi produce spores in slimy, clingy blobs that stick to the bodies of passing insects, thereby ‘hitching a ride’ to other places.

Bread mould, most of the green Penicillium species (from which penicillin is made) and the Aspergillus species do not form their spores inside a structure. The Penicillium species form millions of dry spores in long chains that are very easily distributed by the slightest disturbance in the air. The fungus that appears as little black dots inside dead or discoloured patches on leaves does form its spores within a structure. Often these structures have small openings or necks through which the spores are pushed in little tendrils that can be sticky or dry, and are then dispersed by the wind, rain or insects. The structures of other fungi simply disintegrate to release the spores.