A brief introduction
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Pachytheca in Rhynie chert The nematophytes, which means "filamentous plants", are known for about 150 years as fossils from the Silurian and Lower Devonian but they are still so poorly understood that lately they are not even listed among plant fossils but more cautiously under "Enigmatic Organisms" [1] (**). Their sizes and shapes range from millimeter-size spheres (Pachytheca, see picture) and centimeter-size flaps (Nematothallus [2], Nematophyton and others, see picture below) to meter-size trunks (Prototaxites) [3].
Essentially they are made up of two or more types of filaments which nearly always appear as empty tubes. The tubes typically form a chaotic tangle (*) with a more or less distinct preference for some plane or direction. In some species, part of the filaments are aligned perpendicular to the surface, most perfectly so in the case of Pachytheca. un-named nematophyte in Rhynie chert

Nematophytes are very rare fossils in the Lower Devonian Rhynie chert but the few specimens found lately provide answers to some of the questions lingering in the literature for a long time. However, they pose new questions, too, as it is apparent from the picture below right.
nematophytes from the Rhynie chert represent at least 7 species, among them non-described ones. The tubes of the live nematophytes seem to have been embedded in gel.
The long-standing enigma of an unexpected cellular pattern known as Nematothallus cuticle, often found together with coalified tangles of filaments, is demystified here for the first time. Uncommon Nematoplexus "branch knot"

The much bigger enigma of Prototaxites has aroused the imagination of scientists as well as fossil collectors, giving rise to wild speculations ever since it was discovered up to now (2010). The latest attempt to demystify the great Prototaxites by assorting it with humble liverworts is thwarted here with the help of small nematophytes from the Rhynie chert.
Most of the discoveries and conclusions discussed in the contributions up to Nr. 41 had been presented at EPPC 2010 [4].
Nematoplexus has turned out more enigmatic than previously thought, with details never seen before, as the big "knot" in this image on the right.

On the Aberdeen Univerity website [5], the characteristic feature of Nematoplexus, the spirally wound tubes, is ascribed to virtually all nematophytes. Apparently they did not know Pachytheca with straight tubes and other nematophytes with irregularly wavy tubes, as in the image above.
** Also in [1], chapter on bryophytes, it is proclaimed that "One interesting hypothesis suggests that several of the enigmatic ... nematophytes may represent remains of ancient liverworts ... . ... At least some of the tubular aggregations assigned to nematophytes have been reinterpreted as ... liverwort rhizoids, ... ." That hypothesis is refuted in
Rhynie Chert News 41.
For new developments see [6] and the discussion in Rhynie Chert News 30.
Listed below are the links to the contributions in
Rhynie Chert News, brief descriptions, and the labels of the samples in the own collection.

  1     Pachytheca, first specimen in chert, central cut       Rh11/1.1
36     Pachytheca, first specimen in chert, off-centre cut  Rh11/1.2
44      Pachytheca – a nematophyte propagule ?                Rh11/1.1

29     Nematoplexus, bigger than type specimem, new species ?  Rh9/86.2
39     Nematoplexus with a wry twist ?                                   [1]  Rh9/86.1
51     spiralling and weakly curved tubes                                      Rh9/86.1,2
71     new type of knot and tubes                                Rh15/79.1,4
102    spirals with 5 turns and various other tubes      Rh15/79.1-4
106   Nematoplexus big and small, new charophyte gametangia, Castracollis    Rh9/86.2
122   Nematoplexus size data, Nematothallus tube wall pattern                           Rh9/86.1,2
  solitary spiral with 3 turns among Palaeonitella         Rh5/3.2
126   enigmatic knots of Nematoplexus from several samples       Rh6/102   Rh9/86.2   Rh15/79.1,2
133   detached spirals near old knot with much narrower tubes emerging    Rh13/35.1
134   spirals apparently emerging from the surface of the knot     Rh15/79.4
135   Nematoplexus  -  thrice enigmatic                                         Rh15/79.1

136   tubes spiralling and straight     Rh9/86.1,2
Nematoplexus surprisingly polymorphic     Rh6/102
Other Nematophytes
13     weft of big tubes, new species ?     Rh13/7.1
30     pseudo-cells "Nematothallus cuticle" explained                      Rh2/81.1
35     flat nematophyte, Nematophyton taiti (?)    Rh2/7.6
38     no liverwort connection of nematophytes and Prototaxites    Rh2/81.1,3
40     shrunken big tubes                                                                   Rh2/81.1,3
41     no liverwort connection of Cosmochlaina and Prototaxites 
46     Nematophyton taiti (?) – details and reconstruction
86     tangle of very thin tubes, 6-8Ám     Rh3/9.1,2
92     glades in the weft of big tubes                                                  Rh2/81.3
98     weft of big tubes in a gel lump with dried-up surface layer    Rh13/7.1,2
99      weft of narrow tubes with peculiar details                               Rh13/1.2
107   first 3D-Nematothallus

H.-J. Weiss          updated 2016, 2017, 2018, 2019,  re-arranged 2019

[1] T.N. Taylor, E.L.Taylor, M. Krings: Paleobotany, Elsevier 2009.
[2]  P. K. Strother: Clarification of the genus Nematothallus, J. Paleont. 67 (1993), 1090-94.
[3]  H. Steur:
[4]  H.-J. Weiss: Enigmatic Organisms  -  Insights derived from new finds, Poster presentation, EPPC Budapest 2010.
[6]  M.R. Smith, N.J. Butterfield:  A new view on Nematothallus: Coralline Red Algae from the Silurian of Gotland.
      Palaeontology 56(2013), 345–357.

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