This stinky guy is called Cystoderma amianthinum (powdery earthcap). It is an indicator of heaths/acid grassland and other acidic, low nutrient environments like old lawns.
Most authors report it to have a pungent "earthy" odour and I can confirm that this is true!
When I first found it, my samples filled both my fridge and home with "eu de grave" for weeks!
Varieties.... or not?
My specimen appears to be var. rugosoreticulatum, named after its distinctively wrinkled cap; a feature lacking in the normal version, the cap of which is simply "powdery".
Apparently all this species varieties are no longer considered to be true variants at the genetic level, but we will leave that one for the taxonomists to argue. Understanding known expressions of morphological variability is important and remains a useful distinction for anyone who might find themselves thinking they
are looking at two different species.
That Earthy Smell
The first thing that came to mind when I first smelled it was this verse from everyones favourite tale of necrophilia, The Unquiet Grave; a Traditional English folk song made famous by 70's prog giants Gryphon (whom I had the pleasure of seeing perform this song at Nene Valley Rock festival in 2024!).
"My lips they are as cold as clay,
My breath smells earthly strong,
And if you kiss these lily white lips,
Your days they won't be long"
Finally, I knew EXACTLY what the writer meant when they wrote "earthly strong".
Apparently the offending compound is called Geosmin - which translates to "Earth Smell".
This is, for those who like chemistry a "sesquiterpenoid derivative". Human noses are EXTREMELY sensitive to Geosmin and we can detect it at 0.4 parts per billion!
This compound is responsible for most biological taste and odour problems in drinking water. It also contributes to petrichor (that earthy smell after rain) and is a key contributor to the "muddy" smell of carp ...and that classic "pond smell".
It is produced in water by cyanobacteria (blue green algae) and in soil by filamentous bacteria of the saprophytic phylum Actinobacteria (and some other groups). The key producer within the Actinibacteria are the Streptomyces genus. The Actinobacteria are a strange group, which grow as branching, filamentous hyphae, in common with the fungi kingdom. Perhaps it represents an evolutionary link between bacteria and fungi?
If you give it an analytical whiff, you will find it doesn't smell by itself like either petrichor or carp...BUT you will be able to undeerstand how it forms PART of those smells. Then in future, when you smell a fishing lake, or that smell after the rain, you will be able to isolate the Geosmin component!
Cool eh?
Invertebrate Interactions
Geosmin (alongside the second component of petrichor, 2-methylisoborneol (2-MIB)) is a "potent attractant" for the springtail "Folsomia candida" (tiny arthropods that live in soil and leaf litter). As geosmin is produced primarily during Streptomyces sporulation, it is thought that this relationship must have some function in spore dispersal.
And indeed, experiments have shown that colonies deficient in Geosmin spread less widely than those exposed to natural levels.
This interaction is thought to be a symbiotic relationship. The spores adhere to the body of the springtail and are excreted in faeces. The springtail gets fed and in return spreads the bacterium farther than it ever could by itself.
Finding all these invisible links in the system never fails to fascinate me!
But wait, there is more!
Some mosquitos are attracted to it and some ants preferentially colonise Geosmin rich soils, where lower populations of entomopathogenic soil fungi (which attack invertebrates) allows them to enjoy higher survival rates. This is because Streptomyces also produces a range of compunds toxic to fungi, bacteria, nematodes and other species which might otherwise consume it.
Egg laying Fruit flies Drosphilia are actively repelled, yet are attracted at weaker concentrations of Geosmin. It could be that high concentrations could act as a warning signal to sensitive species.
Could this be why some fungi, such a C. amianthinum smell so intensely of Geosmin? Is it a way of repelling invertebrates that might consume it? Or attracting those who may aid in spreading spores?
Fungal Interactions
Finally...and how cool is this?..... it has a parasite in the Squamanita genus, which is very rare and named on the Red List as Near Threatened. It is named very dramatically as The Powdercap Strangler Squamanita paradoxa". It comes up through the stem and becomes a true chimera; replacing the cap with its own violet cap and leaving behind just the scaly orange of the lower stem to show its former identity!
Fungi are SO WEIRD!
Image: First Nature (2004).
What a fun shroom!
Medicinal use of Streptomyces
Compounds produced by Streptomyces have been developed by agriculture and medicine as antibacterials, anti-fungals, anti-parasitics, and chemotherapeutics.
This really drives home the point of how important it really is that we maintain healthy, biodiverse soils, full of thriving biological activity.
Life begins in the soil.
Sources
Photographs: Fay Brotherhood (2023) taken from Bushey, Hertfordshire (other than where indicated otherwise).
hashtag#ecology hashtag#mycology hashtag#botany hashtag#biodiversity
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