Deep-red Psaronius from the Doehlen basin
deutsche Version

Fossil trunks of Palaeozoic tree ferns, known under the collective term Psaronius, are much less abundant than the usual petrified wood but make beautiful sights in exhibitions. Big and beautiful specimens are known from Chemnitz. Less conspicuous but nevertheless interesting are the rare finds from the Doehlen basin: Permian Chert News 6, 9, 12, 25. There, small well-preserved fern pinnules and frond parts had been found and described as "maggot fern" Scolecopteris elegans [1], and many more of them have been found recently. Careless handling of the "maggot stone" problem caused the repeatedly published error that the fossil "maggot ferns" from the Doehlen basin represented only this one species [2,3]. Thorough inspection has recently revealed that they represent more than one tree fern species [4,5,6]. This poses the problem of how to relate the foliage to the trunks, which is not considered here.
deep-red Psaronius
Fig.1: Cross-section of a slightly flattened Psaronius tree trunk fragment with differing aspects of the central part (above) and surrounding aerial root mantle.
Image width 13cm.

Note that the peculiar way of Psaronius growth implies that there is nearly all aerial roots at the base but no such near the top. Hence, the present sample must be a stem fragment from somewhere in between.
(For a concise description of Psaronius growth see [7].)

This sample does not represent a novel red Psaronius but a colour variety of the fossil, resulting from profuse precipitation of hematite during or after silicification. The inhomogeneus distribution of the red stain, mainly in a broad strip along the edge and beside some crack, indicates diffusion in the solid state. The latter follows also from the vanished red stain close to the crack with red surroundings above right. Obviously this crack had favoured the red staining of nearby conducting strands but later enabled the stain to get partially removed. In this sample the aerial roots are (partially) separated from the central part of the stem with its conducting strands by a "palisade wall" of sclerenchyma as in Fig.2. Two aerial roots seem to have just squeezed through. The wall structure can be so vague that it is hardly seen, as in Fig.3. It is seen in a few publications, e.g. [8].

Enigmatic is the similarity of the "palisade walls" in Fig.2 and in an unidentified stem with a wood ring outside [9].
red Ps
Fig.2: Wall separating the central part with conducting strands and the aerial root mantle; detail of the Psaronius cross-section in Fig.1. Image width 17.5mm.

Fig.3 (below): Three aspects of tracheid cross-sections in one picture:
 forming a ribbon-like conducting strand (above), forming a strand inside an adventitious root (below right) with "empty" tracheids, same as before but tracheids with opaque fill (left). Image width 5.5mm.Ps tracheid aspects

The tracheids are thin-walled but may appear thick-walled due to mineral deposits, as seen on the ribbon-like conducting strand cross-section in Fig.3. A few thin-walled ones are seen on the left. The glass-clear fill makes the tracheid sections appear deep dark inside, which also applies to the conducting strand of the aerial root below right in the image.
The distribution of tracheids with opaque fills suggests that the originally clear chalcedony turned opaque under the influence of diffusion from outside and from cracks.

patterned tracheid walls
Fig.4: Longitudinal section of a bunch of slightly bent tracheids with scalariform wall. Image width 1.2mm.

The clear chalcedony inside the tracheids offers a surprisingly detailed view of the tracheid walls in Fig.4. The apparent problems related to the aspect of the tracheid walls have been discussed in
Permian Chert News 25 .
The images show details from two polished cut faces of the sample W/20, found about 1990 by S. Weiss in a patch of glacial gravel on the Wilmsdorf golf course near Freital (Doehlen Basin).

H.-J. Weiss      2022

[1]  E. Zenker: Scolecopteris elegans, ein neues fossiles Farrngewächs mit Fructification. Linnaea 11(1837), 509-12.

[2]  M. Barthel: Die Madensteine vom Windberg. in: U. Dernbach, W.D. Tidwell: Geheimnisse versteinerter Pflanzen. D'ORO 2002. S.65-77.
[3]  M. Barthel: Die Rotliegendflora der Döhlen-Formation. Geologica Saxonica 61 (2) 2015 (2016 erschienen), 105-238.    S.226
[4]  H.-J. Weiss: Scolecopteris synangium stalks – real and illusory., Permian Chert News 4.
[5]  H.-J. WeissMaggot fern disputes., Permian Chert News 24.
[6]  H.-J. WeissMaggot fern confusion., Permian Chert News 26.
[7]  H. Steur:
 The tree fern Psaronius
[8]  B. M. Stidd: Morphology and anatomy of the frond of Psaronius. Palaeontographica B 134 (1971), 87-123, Plate 16 Fig.8.
[9]  H.-J. Weiss: A small seed fern stem..., Fossil Wood News 19.

Scolecopteris pinnule cross-section, Sardinia Permian Chert News39
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