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 unexpected cellular patterns known as Nematothallus cuticles, often seen together with coalified filaments, are tentatively explained here as not related to cells. 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 (as well as thorough investigations ***) ever since it was discovered. The latest attempt to demystify the great Prototaxites by assorting it with humble liverworts (**) has been thwarted  with the help of small nematophytes from the Rhynie chert [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 although it applies to Nematoplexus only.
** 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.
*** Now that the famous nematophyte Prototaxites is interpreted as a huge fungus or lichen [7,8] and the less known small Nematophyton taiti [9] from Rhynie has been re-named Prototaxites taiti [10], the startling question arises whether or not more nematophytes are really fungi or lichens.

H.-J. Weiss          updated 2016, 2017, 2018, 2019,  re-arranged 2019, updated 2020

[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.
[7]  F.M. Hueber: Rotted wood-alga-fungus: the history and life of Prototaxites Dawson 1859. Rev. Palaeobot. Palynol. 116 (2001), 123–158.
[8]  C.K. Boyce et al.:  Devonian landscape heterogeneity recorded by a giant fungus. Geology 35 (2007), 399–402.
[9]  R. Kidston, W.H. Lang : On Old Red Sandstone plants showing structure ...,  Part V.  Trans. Roy. Soc. Edinburgh 52 (1921), 855-902.
[10]  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.

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 tubes than type specimem, new species ?  Rh9/86.2
39     Nematoplexus with a wry twist ?                                        [5]  Rh9/86
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 central clot 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
151   Nematothallus and Nematoplexus in one chert sample     
152   tubes at Nematoplexus knots                                        Rh15/79    Rh14/35
156.  varied nematophytes in Rhynie chert          Rh9/86.1   Rh15/79   Rh2/81   Rh13/7.1   Rh3/9.1   Rh13/1.2   Rh2/7.6
158   Nematophyte tubes and "branch knots"      Rh2/81.3   Rh13/7.1   Rh15/79.4

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     wilting big tubes, decaying organic gel          Rh13/7.2           Rh2/81.1,3
41     no liverwort connection of Cosmochlaina and Prototaxites 
flat nematophyte, Nematophyton taiti (?) – details and reconstruction     Rh2/7.6
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
122   Nematothallus tube wall pattern, Nematoplexus size data,                           Rh9/86.1,2
151   Nematothallus and Nematoplexus in one chert sample     Rh9/86
153   flat nematophyte  -  a fungus ?                Rh2/7
154   big tubes with settled tiny grains inside     Rh2/81.1
155   Nematophyte twice protected                  Rh13/7.2
156.  varied nematophytes in Rhynie chert       Rh9/86.1   Rh15/79    Rh2/81   Rh13/7.1   Rh3/9.1   Rh13/1.2   Rh2/7.6
157.  tracheid-like tubes in Rhynie chert           Rh9/86.1,2      Rh9/33.1
158   Nematophyte tubes and "branch knots"    
Rh2/81.3   Rh13/7.1   Rh15/79.4

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