Scary Nothia 

Nothia section
To those who are acquainted with the Rhynie chert fossils, this headline must seem inappropriate. Every time when a friendly or curiously looking "face" is seen on surfaces or cut faces of Rhynie chert, it is most often a section of the small plant Nothia (Fig.1). One would not have thought that this early land plant had already developed an elaborate technique for scaring off unwelcome guests.

Fig1: Nothia, part of a cross-section of a forking shoot near the point of separation, with sections of big tubes. Width of the picture 4.3mm.


This small Lower Devonian plant is remarkable for a unique feature: big tubes running below the surface, with volumes equalling that of hundreds of normal cells taken together, first discussed in [1] and tentatively  re-interpreted later on the basis of own finds [2]. They are seen here more clearly than usual. They are thought to be filled with some deterrent liquid which spills out when the vessel is tapped, thus repelling small herbivorous creatures trying to suck sap or to get at the spores.

While the shoot in Fig.1 had not yet separated, the central strand had forked twice, with two sections seen here. The big tubes are seen clustering, for whichever reason, at some places at the periphery. Possibly they are about to extend into the capsule stalks and into the capsule walls, where they may cause the imaginative observer to see a scary monster confronting him with 4 eyes which really are tube sections (Fig.2). 
In order to understand what is seen in Fig.2, one should try to imagine the 3D-shape of the spore capsule with a broad slit covered by slightly overlapping and diverging valves forming a kind of broad mouth extending half arond the capsule. Fig.2 may seem confusing because the sample had been cut
incidentally such that the upper valve is seen in cross-section but the lower valve is seen nearly parallel to the cut, owing to its deviating orientation. Hence, the big tubes are seen in cross-section above and in roughly longitudinal section below.
The valves are supposed to separate at maturity so that the spores are released through the resulting gap. In view of the peculiar features, Nothia can be considered a rather advanced early land plant.

Nothia capsule
Fig.2 (right): Nothia sporangium, rare sight with cut face of the sample (picture plane) nearly parallel to the "mouth" front. Width of the picture 2mm.

The idea of the tubes being vessels for deterrent liquid is suggested by three observations:
 - There are no tubes on the lower parts of the plant [1].
 - The tubes seem to have formed by the lesion of the walls of lots of cells
    at or near the surface [2].
 - Lesion of cell walls to make tubes for deterrent liquid is known from
    flowering plants.

The tubes are usually positioned such that only a narrow strip along the epidermis
is seen, as in Rhynie Chert News 57. There, Figs.6,7 indicate the presence of a big tube behind the surface. This is compatible with the tube cross-section in Fig.2, above right. Other tube cross-sections are less distinctly seen here and elsewhere. Some tubes with elliptical cross-section in Fig.1 seem to be positioned below the epidermis.
Nothia section
It is hoped that more details will appear on other Rhynie chert samples which might either support or doubt the poison tube idea. Unfortunately, most sections are of not much use in this connection, like the really scary one on the left.

Fig.3: Nothia cross-section, hollow before silicification, cavity partially filled with crystalline quartz.


H.-J. Weiss       2017

[1]  H. Kerp, H. Hass, V. Mosbrugger: New data on Nothia aphylla,
       in: P.G. Gensel, D. Edwards (eds.): Plants Invade the Land, N.Y. 2001
[2]  Rhynie Chert News 33.


110

Site map
Rhynie Chert News
Rhynie chert