Parasite scabs on Rhynie chert plants
deutsche Version

The Early Devonian habitat preserved in the Rhynie chert is well known among biologists not only for its early land plants but for its abundance of fungus species as well [1]. A very common symbiotic fungus in the early land plants appears as dark fills of cells in a concentric ring on cross-sections, here faintly seen in Fig.1. The majority of fungi in the Rhynie chert are saprophytes. Their hyphae and resting spores seen inside and outside decaying plants are quite common. Quite uncommon is the organism seen here, which apparently causes live plants to grow black mounds without doing much damage.
Parasites on AglaophytonParasite on AglaophytonFigs.1,2:  Tilted cross-section of well preserved Aglaophyton, invaded by an unknown organism interfering with cell growth and producing dark matter.
Frame widths 7mm and 2mm.

As a characteristic feature of the invaded spot, the dark misshapen tissue produces a globular body on top as if it were a propagule. A similar spot is seen on the left of the section in Fig.1. Possibly a globular body had been shed there earlier.
The control of cell growth of Aglaophyton by the parasite is most obvious in Fig.3. Cells in a near-surface region had been induced to grow such that they form a regular mound. The globular objects on top seem to be partially translucent, particulary the one in Fig.5.
It is not known in which way the cavity below the dark spot in Fig.4 may be related to it.

The symbiotic fungus Glomites rhyniensis [1] seen as brown fills in Fig.3 and the parasite on the mound apparently do not mutually interfere.
Annotation: Dark fungus matter inside cells had given rise to a veritable craze of its interpretation as mite coprolites: See Rhynie Chert News 85 .

Ag AgAg
Figs.3-5:  Mounds grown on the surface of Aglaophyton due to a parasite interfering with cell growth.
Frame widths 2mm.

Rh scab

Fig.6: Parasite with globule on the surface of Rhynia. Frame width 1mm, same scale as Figs.2-5.

The tissue in Fig.6 is poorly preserved so that an infection of live Rhynia is not evident here. Doubtless it is Rhynia because there are no other plants in this sample. Globules like these must not be confused with the often abundant warts on Rhynia (Rhynie Chert News 159), which may appear as nearly globular in rare cases.
In view of other cases of plant growth being interfered with by fungi, this parasite, too, is probably some fungus.

Samples: Figs.1,2,5: 
Rh2/237.2 (0.2kg) found in 2014;   Fig.3: Rh2/4.3 (2kg) obtained from Shanks in 1998;   Fig.4: Rh2/73.2 (0.29kg) obtained from Shanks in 2002;   Fig.6: Rh22/4.2 (70g) found at Castlehill in 2009.

H.-J. Weiss       2020

[1]  T.N. Taylor, M. Krings, E.L. Taylor:
Fossil Fungi. Elsevier 2015.

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