An uncommon type of Syringodendron
deutsche Version

The ancient relatives of the extant clubmosses, among them the big Sigillaria trees, were part of the coal swamp vegetation [1]. There were several species distinguished by the arrangement and shape of their leaf-scars on the stem surface. The stems often seem to
somehow have lost an outer layer with the leaf scars before fossilisation. The partially decorticated stems show another aspect, called Syringodendron (see image). It can be expected that there are at least as many different Syringodendron patterns as there are Sigillaria species.
The elements of the Syringodendron pattern (also called scars here for short) are doubtless related to the veins running from the inner stem to the leaves but their large size suggests an extension by other tissue. Usually they come in pairs, and the pairs come in files.
Syringodendron, uncommon form
Photograph: Syringodendron pattern on the surface of a sample of soft laminated gray chert with compressed plant debris, angular fragment of a chert layer, with glossy faces; Nobitz gravel pit (NW-Saxony, Germany), probably Upper Carboniferous or Lower Permian. Height of the picture 6.5cm.

The present specimen is special: It does not prompt the idea of a file of pairs but of a pair of chains, which is brought about by three features which, in this combination, are apparently not observed with other forms of Syringodendron:
(1) The lateral spacing of the paired scars is wider than the width of the scars.
(2) The gaps in the file are much smaller than the length of the scars.
(3) The scars are almond-shaped.

Several Syringodendron specimens from the Carboniferous of Villablino, Spain, are similar to the present one but differ in (1) or (2) [2].

The depth of the relief with the scars on the surface of this sample is up to 1mm. A surface layer of about the same thickness has an inconspicuous texture along the stem direction. No texture or structure is seen on the scars. What is most peculiar, there is neither a trace of a vein extending into depth below the scars nor of a tree trunk.
The bulk of this sample consists of a laminated sediment with compressed plant debris so closely spaced that it may be called fossil peat. It is a rather soft chert variety, possibly with some percentage of clay minerals, as it is found in the gravel of the Nobitz gravel pit. The low hardness shows as white spots due to impact.

Finally it can be said that this sample poses some questions:
 - Which Sigillaria species is compatible with this Syringodendron pattern ?
 - Why is the pattern preserved as a relief while everything else is squeezed flat ?
 - What became of the rest of the stem ?
As one thinkable option, the stem could have been on top of the sample surface so that the pattern would be only a replica. However, the deep grooves around the scars seem to contradict this. Anyway, the sample remains enigmatic.
Sample:  found by Sieglinde Weiss at Nobitz in 2009, kept in own collection under No/10.

H.-J. Weiss     2011

[1] H. Steur:
quartz crystal with wood inside
Fossil Wood News  10

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