Venation pattern – a distinct feature of Psaronius tree fern pinnules
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An introductory remark is appropriate here to avoid confusion since there are several valid names for different parts of the same fossil plant: The conspicuous trunks with their intricate internal structure are known as Psaronius *. Their foliage has got the name Pecopteris when preserved as a compression fossil but Scolecopteris (which literally means “maggot fern”) when preserved 3-dimensionally with sporangia present. The ambiguities introduced in this way shall not concern us here.
With increasing amounts of "maggot stones" from Döhlen basin (Lower Permian) becoming available since 1993 it has become apparent that some features of the “maggot fern” vary within wide bounds: The pinnules may be nearly straight or curved up to half-circular shape. Their margins may be nearly smooth or beset with more or less long and tapering fringes. The number of sporangia fused into a synangium may vary from 3 to 6 or rarely 7, and even for a given number of sporangia per synangium their pattern of arrangement may differ on one pinnule [1].
It will be difficult to find out to which degree such variability is due to environmental factors (sun or shade, more or less wet habitat, salinity of swamp water), age (juvenile, adult, wilting), etc., and which are inherited features. Finding out this might give clues concerning the response to a changing environment, or it might serve as a basis for differentiation between various strains or species.
Scolecopteris with forking veins
There are at least two features which are most likely inherited: (1) the presence or absence of forking lateral veins on the pinnules and (2) the angle between the lateral veins and the pinnule axis. According to Millay [2], forking veins are absent in Sc. elegans and several related species. Scolecopteris specimens with forking veins are not rare among those recently found in Döhlen basin, which is incompatible with the claim in [3,6] that all recent finds belong to Scolecopteris elegans.

Fig. 1:  Pinna of Scolecopteris with both forking and simple veins on the pinnules.
Width of the picture 6mm.



Although much more structure information can be preserved in chert compared to coalified compressions, the vein pattern of the chert specimens is less conspicuous because the fronds and their parts are usually not lying flat in the chert but in tilted and distorted positions. Even in the rare cases where pinnules form a surface relief, the vein pattern is usually seen less distinctly than on the often larger frond parts found as compression fossils. However, there are chert samples with largely decayed plant matter where virtually nothing is left but a few forking veins revealing the presence of fern foliage.
When trying to measure the angle at which the veins branch off, one encounters more difficulties: The pinnule shape implies that the veins are not curves in a plane but in space, and their curvature tends to vary shortly after branching off from the midvein. In order to agree upon a simple procedure of angle measurement, one may choose the tangent to the vein at a point halfway to the margin, and look at that tangent in top view, which means project it onto the plane of the pinnule. The pinnule, however, is usually not plane, hence one has to take the tangent plane to the pinnule at the position of branching-off for a reference plane. This is about the same what one would perhaps intuitively do without such set of rules but it may be useful to be aware that other rules would produce other values of the angle.

Independent of the details of measurement, a careful look at the veining angles and other features reveals that the literature on Scolecopteris is fraught with a disturbing lot of inconsistencies waiting to be removed.
The venations of Fig.2 and Fig.3 differ significantly. By taking the intuitive approach, one finds angles around 60° in Fig.2 and 45° in Fig.3. Hence, if the angle is typically 60° for Sc. elegans as claimed in [3], the pinnules in Fig.2 may be Sc. elegans but those in Fig.3 are certainly not. (This is also supported by their length of 7mm since the length of Sc. elegans pinnules is 4-5mm [3].) If Fig.3 were Sc. elegans as claimed in [3], Tafel 2, the 60°-rule would not be valid.
What is presented as Sc. elegans in [4], Tafel VII, and [3], Tafel 5, shows veining angles of 45° and other features differing strongly from those of the type specimen (lectotype) in [3], Tafel 1.  45°-venation on alleged Sc. elegans is also seen in [5], Fig.6. (There, "Pecopteris elegans" in the captions of Figs.3,4,6-10 is a mistake.) The pinna in Fig.1 differs from Sc. elegans not only by its forking veins but also by angles smaller than 60°.
When the chert sample with the pinnules pictured in Permian Chert News 1, Fig.1, seen on the raw surface in side view, was recently cut, it revealed pinnules with 45°-venation on the cut face, which is not compatible with its assignment to Sc. elegans in [3].

Scolecopteris with non-forking veins, angle ~60°Scolecopteris with non-forking veins, angle ~45°

Figs.2,3:  Rare examples of Scolecopteris pinnules distinctly seen as reliefs on the surface of a chert layer. Height of the pictures 7mm.






It requires some experience to reveal a vein pattern like the one in Fig.1 by carefully choosing the cut plane of the sample in such a way that as many pinnules as possible are seen in top view. In this connection it is worth mentioning that Gert Müller (Dresden) [7], who found and cut the sample of Fig.1, was the first one to find more “maggot stones” after nearly a century of no finds, thus essentially contributing to the recent upsurge of interest in the subject.

Finally it appears that distinct features of the vein pattern, as forking veins and angles near 45°, provide strong arguments against the interpretation of all recent finds of Scolecopteris in Döhlen basin as Sc. elegans, as claimed in [3,6]. This is supported by other features, as the presence or absence of hairs, long or short pedicels of synangia, enclosed or exposed synangia, and others.

Samples: Old fragments of Lower Permian chert with more or less rounded edges, found among younger fluviatile deposits in Döhlen basin near Dresden, Saxony, Germany.
Fig.1:  Found by Gert Müller  (Dresden) [7] at the type locality of  Sc. elegans near Kleinnaundorf (1985), photograph by H. Sahm.
Fig.2:  Sample W/3.2, own find (1992), Wilmsdorf, golf course.
Fig.3:  Sample H2/35.2, own find (1993), Hänichen.
* Uncommonly big and well-preserved specimens of Psaronius, the stem of several "maggot fern" species, are on display at the Naturkunde Museum Chemnitz.

H.-J. Weiss    2011

[1]  H.-J. Weiss: Beobachtungen zur Variabilität der Synangien des Madenfarns. Veröff. Museum f. Naturkunde Chemnitz 25(2002), 57-62.
[2]  M.A. Millay: Study of paleozoic marattialeans. A monograph of the American species of Scolecopteris. Palaeontographica B169(1979), 1-69.
[3]  M. Barthel, W. Reichel, H.-J. Weiss : "Madensteine" in Sachsen.  Abhandl. Staatl. Mus. Mineral. Geol. Dresden 41(1995), 117-135.
[4]  M. Barthel : Pecopteris-Arten E.F. von Schlotheims aus Typuslokalitäten in der DDR. Schriftenreihe geol. Wiss. Berlin 16(1980), 275-304.
[5]  M. Barthel, H.-J. Weiss: Xeromorphe Baumfarne im Rotliegend Sachsens. Veröff. Museum f. Naturkunde Chemnitz 20(1997).
[6]  M. Barthel: The maggot stones from Windberg ridge, Germany.
      in: U. Dernbach, W.D. Tidwell: Secrets of Petrified Plants. D'ORO Publ. 2002. p65-77.
[7]  
G. Müller:  private communication.
Scolecopteris pinnule cross-section, Sardinia Permian Chert News2

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