Flat nematophyte - Details and reconstruction
deutsche Version
A recently found nematophyte resembling Nematophyton taiti found in the Rhynie chert about a hundred years ago [1] shows a few details from which a tentative reconstruction can be derived. (See also Rhynie Chert News 35
.) Since the nematophytes have not yet been placed on a branch of the phylogenetic tree but go under the haunting term Enigmatic Organisms [2], any new detail will be of interest.
As explained before, nematophytes are made up of tube-like filaments of two or more types, probably embedded in organic gel which keeps them together and keeps floating debris out.

The present specimen shows three types of tissues in a wider sense (Fig.1). There is an inner stratum with big tubes of about 20Ám diameter and probably much smaller tubes, not seen here, in between. This inner stratum is enveloped by a region with poorly visible smaller tubes which mainly appear as scattered dark sections indicating diameters of about 10Ám. Embedded in this outer layer there are pockets of aligned tubes, often in a more or less fan-shaped arrangement, diverging towards the surface (Figs.1,2). Remarkable are the chains of dark dots apparently generated in some of the tubes (Fig.1), with superficial resemblance to ascospores of the ascomycetes.

Fig.1: Nematophyte from Rhynie chert, half vertical section, middle stratum with big tubes below, outer layer above, with pocket of aligned tubes, rows of dark dots therein. Width of the image 1.1mm.
Nematophyton envelope cross-section
Fig.2: Three adjacent pockets of tubes aligned in a fan-like way in the
outer layer of the nematophyte specimen presented here.

Fig.3 (below): Tentative reconstruction based on observed details of the flat nematophyte specimen recently found in the Rhynie chert. Width about 3.5cm.

Nematophyton cross-section, tentative reconstruction
The reconstruction is based on a specimen which is not preserved as a whole but as several fragments (in one piece of chert) which seemed to have belonged to a patch with a diameter of about 3.5cm. The "branch knots" seen among the big tubes in other nematophytes seem to be less conspicuous here.

Although of no relevance to the present reconstruction, it is worth mentioning that the tube sizes of several nematophyte specimens from the Rhynie chert differ considerably. The diameter of the aligned tubes is about 10Ám in this specimen, about 20Ám in Pachytheca, and about 60Ám in the specimen shown in 
Rhynie Chert News 92.
It can be hoped that observations like the present ones will gradually contribute to a better understanding of the nematophytes so that they eventually don't have to carry the epithet "Enigmatic Organisms" any more.
Annotations 2020: The flat shape seemed to hint at a possible connection with Nematothallus [4]. That idea is herewith retracted since a small lump of a nematophyte which might be Nematothallus after [3], preserved in 3D, has been found recently: Rhynie Chert News 151.  (Sorry, Nematothallus and Nematophyton had been confused in the first version of the above text.)
Now that Nematophyton taiti [1] has been re-named Prototaxites taiti [5], the present specimen, too, may have to be reconsidered with respect to a possible fungus affiliation.
More unknown nematophytes are compiled in Rhynie Chert News 156 . 
Sample: Rh2/7 (2.1kg), obtained from Shanks in 2000, Fig.1 taken from Part 6.

H.-J. Weiss      2011    2020   

[1]  R. Kidston, W.H. Lang: On Old Red Sandstone plants showing structure ..., Part V,
      Trans. Roy. Soc. Edinburgh 52 (1921), 855-902.
[2] T.N. Taylor,  E.L.Taylor, M. Krings: Paleobotany, Elsevier 2009.
[3]  P. K. Strother: Clarification of the genus Nematothallus, J. Paleont. 67 (1993), 1090-94.
[4]  H.-J. Weiss: Enigmatic Organisms  -  Insights derived from new finds, Poster presentation, EPPC Budapest 2010.
[5]  R. Honegger, D. Edwards, L. Axe, Ch. Strullu-Derrien: Fertile Prototaxites taiti: a basal ascomycete with inoperculate, polysporous asci lacking croziers.
      Phil. Trans. Roy. Soc. B 373 (2017): 20170146.
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