Scolecopteris synangium stalks –  illusory and real ones
deutsche Version

As a characteristic feature of marattialean ferns, fossil and extant, the sporangia are fused into entities called synangia attached to the pinnule with a stalk or pedicel which may be so short that it is hardly visible. After having seen lots of silicified specimens of Scolecopteris, the best known fossil marattialean fern, which is known with several species, one wonders what to think of the long synangium stalks of Scolecopteris elegans pictured by Zenker [1], who had described this species first in 1837 (Fig.1). His observations were based on the "maggot stones" from the Lower Devonian Döhlen basin, hence the name Scolecopteris, literally maggot fern.
Scolecopteris pinnule with illusory synangium stalks
Fig.1: "Zenker's tulip bed": Pinnule with synangia, allegedly with long stalks [1]. The stalks are explained here as artifacts.

The conspicuous stalks in Fig.1 are certainly not real, as suggested by own finds (Fig.2). Obviously, Zenker regarded them as real as he added slender stalks to all synangia drawings.
Scolecopteris, formation of illusory synangium stalks
Fig.2: Illusion of slender synangium stalks brought about by partial decay of sporangium tissue, the successive stages of which are preserved in this chert sample from Döhlen basin with a rare variety of Scolecopteris with exceptionally small sporangia. Width of the picture 2mm.

Apparently, the narrow central strand of the broad and very short pedicel extends between the sporangia, then somehow diffuses and blends into the inner linings of the sporangia. It is more resistent to decay than parts of the synangium are, thus appearing as a slender stalk [9].
The illusion of longer pedicels is also produced by partial decay of pinnule tissue, as in [2], Fig.11.90, while the true size of the pedicels is clearly seen on other pinnules in that picture of a sample from Döhlen basin, the type locality of Scolecopteris, the "maggot fern".
Judging from the small fraction of synangia incidentally cut into halves lengthwise so that the pedicel is distinctly seen, most of the recent "maggot fern" finds in Döhlen basin show very short broad pedicels (Fig.3) like those pictured by Strasburger [3] in 1875, (Fig.4). Pinnules with such aspect had been assigned to Sc. elegans [3,4]. However, pinnule size and venation of own finds lead to the assumption that pinnules as in Figs.3,4 represent at least one more species in addition to Sc. elegans

Scolecopteris pinnule cross-section, 1999Scolecopteris pinnule cross-section, 1874Scolecopteris pinnule cross-section after lectotype, 1995
Figs.3-5: Scolecopteris pinnule cross-sections with short broad pedicel of the synangia. Fig.3 (far left): recent find. Fig.4: drawing in [3],
apparently idealized. Fig.5: drawn after lectotype in [4], width 2mm.


Now that the slender stalks have been recognized as artifacts emerging after decay of surrounding tissue, pinnules with stout real stalks (Figs.6-8) from the type locality of the maggot fern pose a problem: They differ so much from those seen on the type specimen of Sc. elegans (Fig.5) that they certainly represent another species.
Scolecopteris pinnule lengthwise section, distinct synangium stalksScolecopteris pinnule cross-sections, distinct synangium stalksScolecopteris pinnule cross-sections, distinct synangium stalks

Figs.6-8: Pinnules with conspicuous synangium stalks from the type locality of Scolecopteris elegans but differing distinctly from those of the lectotype of Sc. elegans (Fig.5). Figs.6,7: recent finds. Fig.6: cut lengthwise, Fig.7: pinnule width 1.7mm.
Fig.8: offered as Sc. elegans in [4], Tafel 5, and in [5], Tafel VII; pinnule width 1.9mm.

Fig.7 leads over to a peculiar discrepancy: Pinnules of similarly odd aspect (Fig.8) are presented as Sc. elegans in the very publication [4] where a sample with pinnules like Fig.5 is declared the lectotype of  Sc. elegans. The contradiction becomes even more obvious by the fact that the veining angle on the pinnules of Fig.8 is 45° as seen in [4], Tafel 5, and more clearly in [5], Tafel VII, but that of  Sc. elegans is about 60°, according to [4]. Ignoring the obvious differences, one of the authors [4], M. B., insisted on the inclusion of a statement that there is "complete agreement of all features" between the specimens seen in Figs.3-5 and in Fig.8. The similar statement that there is "most probably only one Scolecopteris species" in the Döhlen Basin has found its way into a monograph [7].

So it appears that, by paying attention to the synangium pedicel, some problems concerning the "maggot fern" Scolecopteris elegans from the type locality have disappeared but others have emerged, and conclusions can be drawn which contradict views repeatedly upheld in the scientific literature:

(1) Very short (< 0.1mm) synangium pedicels as in Figs.3-5 are the most common ones.
(2) Decay of tissue such that the conducting strands are laid bare produces the illusion of stalks, which is the cause of the repeated misinterpretation 
as slender synangium pedicels.
(3) Judging from other features of the foliage it can be concluded that synangia with very short pedicels represent more than one species.
(4) There is fern foliage with long stout synangium pedicels which apparently cannot be derived from the usual short pedicels in any way. Hence they should be regarded as representing another species.

Finally it can be stated that the presence of possibly three more maggot fern species at the type locality of Scolecopteris elegans is suggested by evidence involving synangia and other features of the foliage. This is not surprising in view of the fact that 26 Euramerican Scolecopteris species had been distinguished by 1996 [8], and  likely there will be
more. Repeated attempts to interpret the variety of shapes as being due to the variability of one species appear futile if the available fossils are carefully inspected.

Samples: Figs.2,3,6,7: own finds. Fig.3 is drawn after the sample H2/35.1 pictured in [6], Figs.7,10,  there misnamed Pecopteris and with mistaken scale: The real magnifications are 45x and 10x  instead of  50x and 22x.

H.-J. Weiss    2011


[1]  E. Zenker: Scolecopteris elegans, ein neues fossiles Farrngewächs mit Fructification. Linnaea 11(1837), 509-12.
[2]  T.N. Taylor, E.L. Taylor, M. Krings:  Paleobotany, Elsevier 2009.
[3]  E. Strasburger: Über Scolecopteris elegans ..., Jenaische Z. Nat. N.F.1 Jena 8(1874), 81-95.  
[4]  M. Barthel, W. Reichel, H.-J. Weiss: "Madensteine" in Sachsen.  Abhandl. Staatl. Mus. Mineral. Geol. Dresden 41(1995), 117-135, Table 1.
[5]  M. Barthel: Pecopteris-Arten E.F. v. Schlotheims aus Typuslokalitäten in der DDR, Schriftenreihe geol. Wiss. Berlin 16(1980), 275-304.
[6]  
M. Barthel,  H.-J. Weiss: Xeromorphe Baumfarne im Rotliegend Sachsens.  Veröff. Museum f. Naturkunde Chemnitz 20(1997), 45-56.
[7]  M. Barthel: The maggot stones from Windberg ridge. in: U. Dernbach, W.D. Tidwell: Secrets of Petrified Plants, D'ORO Publ., 2002. p. 65-77.
[8]  M.A. Millay: A review of permineralized Euramerican Carboniferous tree ferns. Rev. Palaeobot. Palyn. 95(1997), 191-209.
[9]  
H.-J. Weiss:  Fehlgedeutete Strukturen in Hornsteinen  -  alte und neue Beispiele. 5. Hornsteintreffen, Museum f. Naturkunde Chemnitz 2006.

Scolecopteris pinnule cross-section, Sardinia Permian Chert News 4

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