Conspicuous in the chert - synangia of Scolecopteris
deutsche Version

Parts of the large fronds of the Psaronius * tree ferns are well-known fossils from several locations worldwide, and they are abundant in some of the chert variants from the Lower Permian Döhlen basin. When preserved 3-dimensionally, as in chert, they are called Scolecopteris, else Pecopteris. As a characteristic feature they bear groups of sporangia fused at their base, called synangia, on the lower side of the pinnules. The build of the synangia is not uniform among the species of
Scolecopteris: They may be thin-walled and largely enveloped by the recurved margin of the pinnule and thus protected (Fig.1), or free-standing and thick-walled (Fig.2), thus protecting themselves, or something in between. The more thick-walled forms were probably hard and dry like the seed capsules of many extant flowering plants and therefore decaying more slowly than the pinnules bearing them. Therefore the synangia are often the most distinctly seen parts of the whole plant. This should make them suitable for the identification of species.
Scolecopteris pinnule in Permian chert, cross-section, Perdasdefogu, Sardinia
Fig.1: Scolecopteris pinnule cross-section with synangia protected by fringes extending from the pinnule margins, seen on the natural surface of a chert layer fragment found near Perdasdefogu, Sardinia, and resembling Sc. elegans, a common species from Döhlen basin. Pinnule width 1.7mm.
Scolecopteris pinnule in Permian chert, cross-section, less-common variety
Fig.2: Scolecopteris pinnule cross-section with exposed synangia composed of thick-walled sporangia, less-common variety from Döhlen basin, drawing after polished chert face. Width of the pinnule 1.6mm.

The identification of species by their synangia turns out less practicable than expected, with the problems being partly genuine and partly generated by palaeobotany itself. The scarce fossil material available to some researchers in this field led to the statement that the synangia of the "maggot fern" Scolecopteris elegans were composed of 4 to 5 sporangia and had "radial" or "bilateral" symmetry. Such statements, by repeated quotation, have found their way into the latest publications on the subject [1,2,3] despite of glaring evidence for the contrary: Symmetry is no useful concept here since synangia of various symmetry types, including no symmetry at all, are usually found together on one pinnule (Figs.3,4 ), and the number of sporangia varies between 3 and 6 (Figs.3-8), with rare cases of 2 and 7. This should have been a well-known fact since the early work by Zenker [4], who found the absence of a common symmetry so remarkable that he drew a variety of synangium cross-sections, including non-symmetrical ones. Zenker was readily referred to for the introduction of the name Scolecopteris but apparently his paper [4] was not thoroughly inspected. Scolecopteris synangia with 3 to 5 sporangia

Scolecopteris synangia, different arrangement of sporangia
Fig.3,4: Usual aspect of Scolecopteris synangia in cross-section:  symmetry of various type or absent. Photographs: H. 
Fig.3 (left): The two rows of synangia below are on one pinnule. They have been cut more or less near their tips.
With of the picture 1.23mm.

Another inappropriate notion surviving in the literature on Scolecopteris is that of "spindle-shaped" or fusiform sporangia [3] although the cross-sections of the sporangia are not even approximately circular, as seen here.

drawing of synangia cross-sections seen in photographnumerous Scolecopteris synangia sectionsFigs.5,6: Chert face with conspicuous array of Scolecopteris synangia cross-sections on pinnules hardly visible owing to decay [5]. Only the well seen cross-sections in Fig.5 have been included into the drawing. Width of the picture 9mm.
Photograph: W. Schwarz.

The good visibility of the synangia in Fig.5 may be due to the higher decay resistence of the possibly dry and hard sporangium walls compared to the soft pinnule tissue. There is something else which is remarkable about Fig.5: Among the 65 synangia seen here in cross-section, 25 are less-common ones with only 3 sporangia, and none is seen with 5.
The large number of synangia can easily mislead to the guess that Fig.5 is possibly a representative part of the sample with a particular species whose synangia are composed of 3 and 4 sporangia only. However, there are synangia with 5 sporangia outside the frame of the picture, which may serve as a warning not to draw conclusions hastily. This applies also to the preliminary statistics in the table below, based on 69 chert samples with synangia seen in cross-section.
The numbers n of the n-fold synangia seen in one chert sample are listed in the first line of the table. The second line is the number of related samples.

  3 4    3 4 5   3 4 5 6    4     4 5    4 5 6   4 5 6 7    5 6    5 6 7   
   14       10        3       15     19       5          1          1        1    

Note that this does not mean that a type characterized by 4-fold synangia
only has been found in 15 samples. Additional cut faces would probably provide synangia with n = 3 or 5 .
As a general observation from the Döhlen basin, synangia with 4, 5, and 6 sporangia are often seen in close vicinity, on the same or neighbouring pinnule (Fig.7).
Most sporangia were empty when the fronds or pinnae fell into the water and became silicified but some were still filled with spores (Fig.8). Here, the spores are not lying in the sporangia loosely but are seen to be still arranged in some original order. As another remarkable feature of the sporangia in Fig.8, the walls have completely collapsed where they mutually touch so that they are seen in cross-section as a mere thin line. (Compare Figs.4,7 where the individual walls are still seen.)
5 Scolecopteris synangia of diffent build on neighbouring pinnulesScolecopteris synangium with spores in every one of 6 sporangia
Fig.7 (far left): Scolecopteris synangia of different type on neighbouring pinnules, as seen on the raw surface of a chert sample. Width of the picture 2.2mm.
Fig.8: Synangium with sporangia completely filled with immature spores and with walls partially collapsed into thin foils. Width of the synangium 0.9mm.

The observations lead to the conclusion that notions like symmetry of the synangia and spindle shape of the sporangia are not helpful for the identification of Scolecopteris elegans and for differentiation between similar strains closely related to it. "Rotational symmetry", which means an n-fold rotational axis in the synangium, is a characteristic feature of a group of Scolecopteris species including Sc. globiforma and Sc. unita [6] but not of Sc. elegans.

Other features of the synangia are more suitable for differentiation between maggot fern variants or species: The pedicel is usually much shorter than wide and thus hardly visible, or it can be rather conspicuous. The sporangia can be thick and short or narrow and tapering.  Hairs on the sporangia are well known from Scolecopteris species found in "coal balls" in North America [7] but have been found in the Döhlen basin in only two samples hitherto. An evaluation of the more useful but rare or elusive features of the synangia in the cherts of the Döhlen basin has not yet been done. Considering that lots of chert samples with Scolecopteris recovered in the 1990s have been stored away and not even looked at, it is well possible that some correlation between synangia features and fern variants will be found when the samples are thoroughly investigated.

Samples: own finds if not indicated otherwise.                Figs. 2-8:  
Döhlen basin, Freital
Fig.1: Pd/2.1, Perdasdefogu, Sardinia, 2009,
Fig.2: Bu4/31.1,  found in 1996
on the property of Lippert, Burgk, Bernhardts Weg 25.
Fig.3-6: Bu10/7,  provided by H. Nitzsche,
 Burgk, Kohlenstr. 24, in 1998.
Fig.7: Bu8/18,   found in 1997 at
Burgk, Am Seilerschuppen, and kept by U. Wagner.
Fig.8: Bu2/5.1,   found in 1995 as one of the first own finds on the "maggot stone" site,
   on the property of W. Netzschwitz 
Kleinnaundorf, Kohlenstr. 23, and kept there.
* 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
, amended 2012

[1]  M. Barthel, W. Reichel, H.-J. Weiss: "Madensteine" in Sachsen.  Abhandl. Staatl. Mus. Mineral. Geol. Dresden 41(1995), 117-135.
[2]  R. Rößler : Der versteinerte Wald von Chemnitz, 2001.
[3]  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.
[4]  E. Zenker: Scolecopteris elegans, ein neues fossiles Farrngewächs mit Fructification. Linnaea 11(1837), 509-12.
[5] H.-J. Weiss: Beobachtungen zur Variabilität der Synangien des Madenfarns. Veröff. Museum f. Naturkunde Chemnitz 25(2002), 57-62
[6] M.A. Millay, J. Galtier: Studies of paleozoic marattialean ferns:  Scolecopteris globiforma from the Stephanian of France.
   Rev. Palaeobot. Palyn. 63(1990), 163-171.
[7]  M.A. Millay: Study of paleozoic marattialeans. A monograph of the American species of Scolecopteris. Palaeontographica B169(1979), 1-69.
Scolecopteris pinnule cross-section, Sardinia Permian Chert News 5

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