Rhynia enigmas old and new
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Rhynia inclined cut with warts
The enigmas concerning Rhynia are of quite different kinds. The first one is obsolete now that it is known that those ones of the abundant plant fossils in the Rhynie chert originally called Rhynia [1] belong to two species. The bigger and more abundant species has got the name Aglaophyton but the smaller and less abundant one has retained the name Rhynia.

As a peculiar feature of the latter, wart-like protrusions are not seldom seen on the cylindrical surface, usually no more than one on a section but most often none at all. Hence, the occurrence of several warts on one section as in Figs.1,2 is exceptional. Their purpose is uncertain but a proposed interpretation in [2], supported by a convincing image, seems to come close to the truth: "They could have been small organs from which root hairs grew when the plant was touching the ground". The warts seen on the numerous own Rhynia sections, however, have not yet revealed another case of unicellular root hairs grown from them.
Usually the warts seem to be sparsely and randomly distributed on the cylindrical surface of the Rhynia stems. Seldom but apparently more often than expected, two of them are seen in opposite positions on the stem, as in Figs.1,2. It is not known whether this is merely incidental.

Fig.1: Inclined sections of Rhynia with wart-like protrusions. Image width 10mm.

Rhynia cut lengthwise with warts

Fig.2: Lengthwise section of Rhynia with wart-like protrusions. Image width 5mm.

Note that the scale of Fig.2 is twice that of Fig1. The stem diameter in Fig.1 is rather big, about 2.4mm, but the one in Fig.2 is rather small, about 0.8mm. Usually the diameter is 1-2mm. Such variability is well known with Rhynia. The slanting cut in Fig.2 above right shows the tissue structure of the outer regions of a bigger stem.
A small wonder in connection with this sample may be briefly mentioned here: It is the conspicuously different mineralisation of two Rhynia stem parts having lain side by side in the siliceous water in the Devonian but looking quite different in the chert now: Fig.3. This phenomenon does not seem to be restricted to Rhynia but is particularly well seen here, along with but unrelated to the enigmas of this chert sample as illustrated in Figs.2,4.
Rhynia yellow and darkRhynia with worm-like tubes

Fig.3 (left): Differently mineralized Rhynia.
Image width 5mm.

Fig.4: Section of Rhynia with wart-like protrusions and big hole with unique worm-like objects. Image width 5mm. 

Fig.5 (below right): Worm-like objects in Fig.4. Image width 2mm.

The structure seen in Figs.4,5 is possibly the most enigmatic one. From the observation that big cavitiesRhynia with warts, big hole, worm-like tubesApparent structure in worm-like tube in Rhynia inside Rhynia are apparantly never related to warts on the surface, it may be concluded that the combination seen here is incidental and hence irrelevant. The unique combination of the big cavity with worm-like limp objects of 0.12-0.18mm width suggests a causal connection in the way of "worms eat Rhynia tissue and leave a big hole". This seemingly simple idea, however, is questioned by the fact that the tubes do not readily reveal creature-like details. They are not torn like moults when strongly bent. They seem to be structureless inside, perhaps with the exception of a poorly preserved one (Fig.6), which contains a lengthy structure looking like a rugged tube of about 20Ám diameter, possibly the gut or axis of some creature.

Fig.6, detail of Fig.5: Worm-like object, apparently revealing some indistinct structure inside. Image width 0.67mm.

So it appears that one small piece of Rhynie chert may reveal peculiar phenomena of quite different nature which contributes to the fascination with the chert but possibly also to confusion. Comparison with other samples, of course, can be helpful but more often than not some problems remain unresolved as long as no comparable fossil matter is available.

Samples:   Fig.1: Rh12/150 (0.64kg) found in 2007, Part 2;   Figs.2-6: Rh16/6 (0.37kg) found in 2008, Part 3.

H.-J. Weiss       2020

[1]  R. Kidston, W.H. Lang : On Old Red Sandstone plants showing structure from the Rhynie Chert bed, Part I,
      Trans. Roy. Soc. Edinburgh 51(1917), 761-84.

[2]  H. Steur: Hans' Paleobotany Pages. steurh.home.xs4all.nl, Rhynia gwynne-vaughanii .
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