Slime Moulds

Slime moulds occasionally cause concern when they appear on plants, but they do not attack or kill the plant.  They vary greatly in their colour, size and form. Their spore-producing structures are often very fragile, disintegrating when touched. 

 

<EM>Mucilago crustacea</EM> on <EM>Hedera</EM> (Ivy)
Mucilago crustacea on Hedera (Ivy)

Quick facts

Common name: Slime mould
Scientific name: Various, but by far the largest sub-group seen in a garden are acellular slime moulds called myxomycetes
Plants affected: Various
Main symptoms: Slimy growths, often on lower stems
Caused by: Slime moulds
Timing: Present year-round, but most likely to be seen in late summer / early autumn
 

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What are slime moulds?

‘Slime mould’ is an informal name given to several kinds of unrelated organisms that can live freely as single cells, but some can also clump together to form larger structures (plasmodia).  Once considered to be fungi, slime moulds are now recognised as a completely different kingdom of single-celled organisms, called protists, that more closely resemble amoeba.   There are some 900 known species of slime mould worldwide, and there are likely to be hundreds more unknown species. They vary greatly in their colour, size and form.​

Slime moulds typically occur in cool, moist, shady places like crevices within decaying wood, beneath the partially decayed bark of logs and stumps, and in leaf litter on the forest floor. However, some are found on live plants, typically on the lower stems, as well as lawns.  A few species can be found in aquatic habitats, alpine areas and desert environments.

Symptoms

  • Slime mould plasmodia (see 'Biology' section, below) are very variable in appearance, depending on the species.  They can be colourless, or come in a range of colours, including yellows, oranges and reds.  The plasmodium constantly changes its’ shape as it creeps along, and is sometimes seen as a slimy ‘sheet’, or a network of strands, on the soil, grass or stems and lower branches of plants. 
  • The spore-producing structures (fruiting bodies) of slime moulds are seen as clusters of tiny nodules on the plasmodium surface, sometimes held on stalks (typically no more than 1-2 mm tall); often in the form of tiny goblets, globes or plumes. They can appear quite suddenly, sometimes overnight.  Slime moulds commonly produce masses of tiny, black spores as their fruiting structures disintegrate, which are mostly wind-dispersed.  Once the fruiting bodies have formed and the spores dispersed, the plasmodium will disappear.
  • Although very small, the fruiting bodies can look quite spectacular, as seen in this collection of photographs
  • May be confused with:
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Unknown slime mould on Heather. Image: RHS.
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Slime mould (unknown) on Rosa. Image: RHS
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Mucilago crustacea. Image: RHS / Beatrice Henricot
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Unknown slime mould on Heather. Image: RHS.
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Slime mould (unknown) on Rosa. Image: RHS
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Mucilago crustacea. Image: RHS / Beatrice Henricot
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Control

No control of this fascinating group of organisms is required, as they are completely harmless and contribute greatly to garden biodiversity. The slime mould is simply using plant stems and other upright structures as a support on which to produce its fruiting structures, and to gain height for efficient spore dispersal. Slime moulds will often vanish as quickly as they have appeared, as the spores are released and the structures disintegrate.  However, if they are considered particularly unsightly they can be dispersed with a jet of water.

Biology

Slime moulds do not attack plants, but obtain their food by engulfing bacteria, fungal spores and other tiny pieces of organic material as they move. Some slime moulds spend most of their life as single-celled, amoeba-like structures, invisible to the naked eye. Others form structures called plasmodia which creep about over the surfaces of materials, engulfing materials including bacteria, spores of fungi and plants and particles of non-living organic matter. At some point, plasmodia convert into spore-bearing structures that resemble those of the true fungi.  Their spore-producing structures are often very fragile, disintegrating when touched.
 
Slime moulds are triggered into spore production by environmental conditions. When food supplies begin to wane the plasmodium migrates to the surface and produces fruiting bodies, which are the fungi-like structures that we find.  The fruiting bodies produce spores which germinate into the single-celled structures, beginning the life cycle again.  The spore-producing structures may develop throughout the year, but are found most commonly in late summer and autumn.
 
The spores of many slime moulds are extremely resilient and can survive in a dried-out form for many years before germinating.  Equally, if conditions become get too wet, the single celled units grow flagella (tails) and switch to a free-swimming cell form.
 
Slime moulds have been used in some incredible practical applications, including urban transport mapping simulations and in the search for dark matter!

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