Fungus-related fossil spheres in Rhynie chert
deutsche Version
The Rhynie chert, famous for its wealth of Lower Devonian fossils, offers also spheres of various size, apparently most of them at the end of some fungus hypha and known as chlamydospores or resting spores, possibly meant to survive unfavourable seasons. They are easily recognized as such if the attached hypha is visible (Fig.1) but most often the site of attachment is not in the picture plane or the hypha had decayed before silicification (Fig.2). The several different resting spores corresponding to the several fungus species "cannot yet be assigned to a particular clade with certainty, as important parts of their life cycles have not yet been discovered"[1].
chlamydosporeresting spores
Fig.1 (far left): Chlamydospores of some saprophytic fungus among remains of early land plants.
Image width 0.6mm.

Fig.2: Chlamydospores of some saprophytic fungus, with stains obtained in silicification.
Image width 1.4mm.  

Usually the content of the chlamydospores had decayed before silicification so that they appear empty or are filled with deposits of different aspect unrelated to the fungus species. From mutual contact between the densely spaced fungus spheres in Fig.2 and their deformation it can be concluded that the spheres in Fig.2 had got unequal stiffness before silicification. The peculiar fact that the stiffness of the sphere is not related to the apparent thickness of the wall is seen on the squeezed sphere in Fig.2 above left, which is deformed likewise by contact with the thin-walled sphere on the left and the thick-walled sphere with red fill on the right.

Much less known than the several chlamydospores are fungus-induced spheres whose generation seems quite absurd: Under the influence of a parasitic fungus a charophyte alga miraculously grew big spheres on thin branches. For reasons unknown, the spheres persisted while the branches decayed, which may mislead to the interpretation as big chlamydospores. Such danger of misinterpretation reduces with the assumption based on observation that interconnected spheres like those in Fig.3 are always modified charophyte parts. The yellow spot with three big spheres attached seems to be the remains of a charophyte whorl of branches.
The spheres emerging from a charophyte alga had probably been water-filled before silicification like the chlamydospores mentioned above, and had become filled with mineral deposits as known from small agates. There must have been two fluid suspensions of dark particles, heavier and lighter than the water inside the spheres. Either suspension had separated itself from the plain water by forming a plane horizontal boundary indicating the orientation during silicification.   spheres on charophyte

Apparently the two smaller spheres above underwent another silicification regime with silica concentration so low that the content did not silicify as a whole but silica became deposited on the walls, thereby forming spherolites resembling glossy pearls.

Fig.3: Well-formed spheres resulting from malformed growth of the charophyte alga Palaeonitella under the influence of the parasitic fungus Milleromyces [2].
Image width 5mm.

One may wonder why fungi produced nearly perfect spheres in quite different ways:
(1) chlamydospores as persistent organs at the ends of hyphae, (2) hypertrophied alga tubes due to the parasitic fungus Milleromyces interfering with the normal growth of a charophyte [2].

Fig.1: Rh2/29.4, obtained from Shanks in 2001;   Fig.2: Rh12/160.9, found in 2007;   Fig.3: Rh14_17.5, obtained from Barron in 2007.

H.-J. Weiss     2022  

[1] T.N. Taylor, E.L. Taylor, M. Krings: Paleobotany,  Elsevier 2009, p76.
[2] T.N. Taylor, M. Krings, E.L. Taylor: Fossil Fungi. Elsevier 2015, p64.
Site map
Rhynie Chert News
Chert formation
Rhynie chert