Enigmatic knots of an enigmatic organism
deutsche Version

knots The wound tubes of the twice enigmatic Nematoplexus [1] mentioned in [2] under the heading Enigmatic Organisms are supposed to be produced inside "branch knots" although branching apparently has never been seen there. What is offered as a branch knot in [2], Fig.6.10, looks rather like a fluid structure governed by surface tension on a substrate with variable wettability, thus being in no way related to the branch knots shown here.
Branch knots of a hitherto unknown type with big tubes have recently been discovered (see
Rhynie Chert News 71 and Figs.5,7,9 below right). They are quite surprising for their features:
 - tube diameters >20Ám, 30Ám at the base,
 - tubes nearly straight or slightly curved,
 - found only in samples with the usual Nematoplexus spirals.

Most often, knots are found among scattered spirals (Figs.1,2). Less often, solitary knots of various aspect are found in areas where regular spirals are absent (Figs.3-9) but usually not far away in the chert sample. (Note that "spiral" is meant here short for "wound in a screw-like way".)
The solitary knots add to the mystery surrounding Nematoplexus. Attached to these knots are tubes differing in shape and size from the "normal" screw-like ones with their remarkably constant curvature and twist, for reasons unknown.

Fig.1: Nematoplexus spirals and parts thereof seen in pale bluish chalcedony; big dark "branch knot", small one near the middle of the image. Note that there is a spiral with three turns above the knot on the left and another one right of the middle, with one tangent of the spiral incidentally being perpendicular to the picture plane so that the spiral looks like an inclined "3". Width of the picture 1.73mm.

Figs.2-9: "Branch knots" of various aspect, with or without spiralling tubes nearby. Same scale as Fig.1, width of the pictures 1.38mm.
knot knot

knot knot

knot knot

knot knot

With the circular cross-sections of the cut-off big tubes in the last image clearly seen, the question arises what the onsets of the tubes inside the knot might look like. Are they all interconnected or did they grow from separate points ? Apparently there is no answer to simple questions of this kind at present. *
Non-spiralling tubes may show
 annular or spiral wall patterns.
Dozens of tubes with patterned wall have been found loosely arranged in a lump resembling Nematothallus (see
Rhynie Chert News 107), only millimeters away from the typical Nematoplexus spirals but in no way connected to the latter. The suggestion that Nematoplexus "may represent the permineralized equivalent of Nematothallus" [2] is not at all substantiated.
As another extension of the Nematoplexus enigma, the regularly wound tubes, too, are occasionally seen with distinctly differing sizes, even at the very same spot of the sample (Rhynie Chert News 106, there Fig.2). Also it appears that tubes with diameters smaller than those of the regular spirals can be weakly curved or nearly straight, like the one seen crossing the last image here. Furthermore, very thin slightly curved tubes (4Ám ?) apparently come out of the big black knot.
One may wonder how the various details thought to be parts of Nematoplexus can possibly be mutually compatible so that they can be regarded as aspects of one species. Otherwise they might represent different species grown very near to each other in places attracting nematophytes. One might even suspect that different nematophytes could have more or less united to form a kind of symbiosis.
In view of the variety of structural features associated with Nematoplexus, it can be expected that this nematophyte will yield more surprises with more finds turning up in Rhynie chert samples stored in collections.
* Annotation 2020: Apparently the tubes seen outside the "knots" had not branched inside. 
Samples from own collection:
Rh6/102 (0.03kg) found by S. Weiss in 2003: Figs.1,5,7;
Rh9/86 (0.28kg) own find in 2003, Part 2: Figs.2,4,6,8 (left column of images);
Rh15/79 (0.27kg) obtained from Barron in 2014, Part 1: Fig.9, Part 2: Fig.3.

H.-J. Weiss       2018  (2nd version)    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 plates.        (Scale error on Plate I Fig.1: not x19 but x1.5)
[2]  T.N. Taylor, E.L.Taylor, M. Krings: Paleobotany, Elsevier 2009.       
(Scale error on Fig.6.9: scale bar not 100Ám, rather 20Ám ?)

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