Devonian fungus globules densely clustered
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Globular organs of several fungi are often seen in the Lower Devonian Rhynie chert. They may be conspicuous, scarce or abundant, and randomly distributed in some places inside or outside plant tissue.
fungus cluster fungus cluster
The pictures, taken from three samples, are of equal scale and width of 1mm. They show fungus globules that are densely packed for unknown reasons.

Fig.1: Coherent cluster of fungus globules, 35-40m, adhering to the surface of Rhynia.

Fig.2 (far right): Cluster of fungus globules, 40-60m, inside degraded Rhynia.

Fig.3 (below): Two clusters of fungus globules, 35-50m, in an area of microbial filaments and networks.

Fungus hyphae are known to thrive inside or near decaying plant matter or even within live plants. They may form vesicles, mostly more or less spherical, often called globules or chlamydospores, a not well defined term. The clusters of fungus globules
in these pictures give rise to wonder.
For no obvious reason, they may stick together closely, as in Fig.1, where they form a lump adhering to the surface of Rhynia which does not show signs of decay. Possibly they are kept in place by hyphae not seen here but what is the advantage of clinging to each other and to a plant that is not decaying ?
Even inside the decaying plant in Fig.2 it remains enigmatic why the hyphae have grown their globules huddled together.

fungus spheresThe globules in Fig.3 have assembled in an area where there is no plant part in the vicinity, only large swaths of filiform and net-like microbes. Again the question arises what the fungus had been feeding on before it became able to grow clusters of spheres.

As a confusing peculiarity, the clusters of this fungus, looked at with moderate magnification as in these cases, may resemble heaps of spores. This visual impression is brought about by apparent markings faintly seen on some of the globules similar to the trilete marks on spores or to the aspect of spore tetrads. These are illusions due to the mostly high transparency of the spheres, as seen, for example, on the sphere at the right edge of Fig.3, where the outlines of two or three spheres in the depth are faintly seen through.
The same effect is also apparent with a picture of Zwergimyces in the latest monograph on fossil fungi [1]. This effect disappears with  higher magnification, where the spheres show lots of detail, including hyphae and a mantle of complex structure [2], but not the illusory markings.
The similarity of this Fig.1 and Fig.6.9 in [1] seems to justify the assumption that the present pictures taken from three samples of Rhynie chert show Zwergimyces, even though Fig.1 and Fig.3 do not support the claim in [1] that "Zwergimyces ... occurs in degraded plant axes ...". Another example of clustering transparent spheres like the present ones has been seen in a microbial lump which apparently had solidified into a miniature reef in the Devonian swamp at Rhynie.
The questions raised above, concerning the reason for the close clustering of globules, also in areas without decaying plants, have not been considered in [1,2]. The possible affiliation of Zwergimyces has remained an unresolved problem, which is discussed in detail in [2].

H.-J. Weiss    2017

[1] T.N.Taylor, M. Krings, E.L. Taylor: Fossil Fungi, Elsevier 2015, p.80.
[2] M. Krings, T.N.Taylor, N. Dotzler, C.J. Harper: Morphology and ontogenetic development of Zwergimyces vestitus ... from the Lower Devonian Rhynie chert.
    Rev. Palaeobot. Palyn. 228(2016), 47-56.

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