Glades in the nematophyte jungle
deutsche Version

Nematophytes are still enigmatic as a whole and in detail as well. One detail, lately seen on a cut face of a Rhynie chert sample with the nematophyte Nematoplexus, incidentally illuminated by the reflected light from a crack and thus visible in Fig.2 of Rhynie Chert News 152, has led to thorough redrafting of this contribution. There one can see how one of the spiralling
Nematoplexus tubes begins without branching at a position which must be at the boundary of a central clot. Hence, the widespread view of the "branch-knots" of Nematoplexus as a tangle of tubes, with "tubes ... entering and leaving" [1], is not true.
(Without branching and without "entering and leaving" tubes, the term "branch-knot" is misleading and should be avoided.)
A comparison of the big clots of this unknown nematophyte, appearing as "glades" in cross-sections, with the small clots in the tangles of Nematoplexus suggests itself. The big clots, too, are not traversed by tubes, and the tubes begin possibly at or near the surface. Apart from the similarities there are obvious differences: These tubes are much bigger, and they are nearly parallel.
nematophyte with clot nematophyte with clotnematophyte with clotnematophyte with clot

nematophyte with clot nematophyte with clotnematophyte with clot

Figs. 1-7: Nematophyte
consisting of rather well aligned tubes,
mainly 50-60Ám across,
randomly distributed between sections
of rounded lumps seen as
"glades" of 0.35-0.5mm
with a frequency of about 10/cm

Fig.3 (in the upper row):
Area with tubes of 15-60Ám width.

The size of every image is 1mm2.

There is no good lengthwise cut of this nematophyte available at present so that evidence of tubes emerging from the clots is poor. A few short tube parts with deviating directions are seen in Fig.2. One or two deviating tubes
in Fig.6 seem to emerge from the surface of the clot (above right). In Fig.7, one tube fits perfectly to the periphery of the clot (above). 
nematophyte tubes
Fig.8: Nematophyte tubes, slightly deranged and separated, thus individually visible in lateral view. 
         The tiny white dots are due to the roughness of the raw sample surface. Same sample and scale as above.

Judging from small fracture faces along the densely spaced tubes which offer a sideways view, even a polished longitudinal section would only offer a confusing assembly of lines with poor contrast which would not look like tubes. Individual tubes can be seen in lateral view if they are displaced and separated by white chalcedony as in Fig.8. The small-scale waviness of the tube walls in Fig.8 seems to indicate that the tubes had been rather soft before silicification, as also observed in Rhynie Chert News 40.
The stronger contrast in Figs. 1-7 compared to Fig.8 does not indicate better preservation or thick-walled tubes but is simply an optical effect. Looking in tube direction in transparent chalcedony makes a sharper contour than looking across. A thin microbial layer would enhance this effect. Other microbial sheets are seen as black lines connecting the tube sections, as in Fig.6.

Annotation 2020: Thanks are due to Gerd Schmahl for microphotographs, particularly for Fig.2 of Rhynie Chert News 152, which has suggested a  re-interpretation of the above pictures. With the assumption that the clearly seen "glades in the nematophyte jungle" are comparable with the less well seen "knots" or "medullary spots" of other nematophytes, one may compare the unknown nematophyte with Nematoplexus and Prototaxites. By doing so, one may conclude that the knots of Nematoplexus have got a definite boundary although it is usually not seen. Also one may guess that the tubes of the above nematophyte and others emerge from the periphery of clots seen here as "glades", also known as "medullary spots".
The much disputed Prototaxites, once regarded as an enormously big nematophyte but lately as a huge fungus or lichen [2,3], raises the question whether or not other nematophytes are rather fungi or lichens. Various nematophytes, including Nematasketum and tubes with sizes like those in Figs.1-8, are presented in [4] and commented on: "However, they are twice the diameter as the skeletal tubes in Nematasketum (Burgess and Edwards,1988)" [4].
It is not attempted here to assign the nematophyte in Figs.1-8 to one of the already described species.

Sample: Rh2/81, 0.63kg, obtained from Shanks in 2003, pictures taken from Part 3.

H.-J. Weiss      2016,   revised in 2020

[1]  A.G. Lyon: On the fragmentary remains of an organism referable to the nematophytales, from the Rhynie chert, Nematoplexus rhyniensis.
      Trans. Roy. Soc. Edinburgh 65(1961-62), 79-87, 2 tables.
[2]  T.N.Taylor, M. Krings, E.L. Taylor: Fossil Fungi. Elsevier 2015.

[3]  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.
P. Filipiak, H. Szaniawski: Nematophytes from the Lower Devonian of Podolia, Ukraine.  
      Rev. Pal. Palyn. 224 (2016), 109-120.

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