Rhynia twice affected
deutsche Version

Cells with dark fills loosely arranged in a concentric circle are occasionally seen on cross-sections of Aglaophyton, less often on those of Rhynia. The dark fills are tangles of fungus hyphae able to penetrate the cell walls [1]. The fungus is assumed to live inside the plant for mutual benefit [2].
The circle of dark dots is seen to be strongly deformed here. In the upper part of the picture it keeps near the circular boundary but in the lower part it is deranged and shifted inward. Obviously the shift is related to the affected area below. Highly peculiar is the rupture of the epidermis with something creeping or growing out. 

Rhynia dryRhynia wet
Figs.1,2: Rhynia cross-section twice affected as seen on the raw surface of a Rhynie chert sample, dry (Fig.1) and wet (Fig.2): dark cells due to the symbiotic fungus Glomites,  enigmatic local parasite effect below.
Image width 3mm.

Fig.3 (below): Detail of the Rhynia cross-section in Fig.2, with ruptured epidermis and something creeping or growing out.
Image width 2mm.

Rhynia wet
Something has come out through the ruptured epidermis and cuticle and has formed a kind of small scab, similar as the small black scabs occasionally appearing on Aglaophyton. There are obvious differences, though: The scabs on Aglaophyton apparently did not interfere with the ring of dark dots in the tissue. What had been the cause of the scab presented here had affected a larger area of tissue, and it must have done so at an early time when the dark cell fills by Glomites had not yet been there. Obviously the later appearing Glomites avoided the yellow area affected by some parasite and placed its dark tangles in cells at some distance.
It may be mentioned here that the diameter of Rhynia is rather large in this sample: 2.8mm. Possible confusion with Aglaophyton seems to be excluded by the presence of the typical warts on the surface of Rhynia (not pictured here), which are abundant on some samples but rare or absent (?) on others.
Sample: Rh7/57 (0.27kg), found in 2003.

H.-J. Weiss    2021

[1]  T.N. Taylor et al.: Fossil arbuscular mycorrhizae from the Early Devonian,
       Mycologia 87(1995), 560-73.

[2]   I. V. Karatygin, N. S. Snigirevskaya, K. N Demchenko:
      Species of the genus Glomites as plant symbionts in Early Devonian ecosystems
     Paleontological J. 40(2006), 572-579.
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