Flat nematophyte - Details and reconstruction
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Nematophyton cross-section details
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 surrounded by an envelope consisting of randomly oriented smaller tubes which mainly appear as dark sections indicating diameters of about 10Ám. Embedded in the envelope layer there are pockets of aligned tubes in a more or less fan-shaped arrangement, diverging towards the surface (Fig.2). Remarkable are the chains of dark dots apparently generated in some of the tubes (Fig.1), with superficial resemblance to ascispores of the ascomycetes.

Fig.1: Nematophyte from Rhynie chert, half vertical section, middle stratum with big tubes below, envelope layer above, with pocket of aligned tubes, rows of dark dots therein. Width of the image 1mm.
Nematophyton envelope cross-section
Fig.2: Three adjacent pockets of tubes aligned in a fan-like way in the envelope 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 3cm.

Nematophyton cross-section, tentative reconstruction

The above 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 characteristic "branch knots" seen among the big tubes in other specimens representing other species seem to be less conspicuous here, which may or may not be merely incidental.
The flat shape of this specimen supports the assumption that Nematothallus*, which is found as coalified patches [3], had not been bulky as suspected of
Nematophyton in [1] but flat before compression. This conclusion had been offered at the EPPC 2010 [4].
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 30. The wound tubes of two own Nematoplexus specimens are twice as big as those of the type specimen.
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.
*(Sorry, Nematothallus and Nematophyton had been confused here in the previous version of this text.)

H.-J. Weiss      2011

[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.

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