Small parts of the large fronds of the well-known Psaronius tree ferns are abundant in some of the chert variants from the Doehlen basin. 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: They may be thin-walled and largely enveloped by the recurved margin of the pinnule and thus protected, or free-standing and thick-walled, thus protecting themselves, or some intermediate form between the extremes may be realized. 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 they are often the most distinctly seen parts of the whole plant. This should make them suitable for identification of species.

However, this turns out less convenient than expected, with the problems being partly genuine and partly generated by palaeobotany itself. The meagre finds available to the early researchers in this field led to the statement that the synangia of the "maggot fern" Scolecopteris elegans were 4-and 5-fold and had "radial" symmetry. This view, by repeated quotation, found its way into the latest publications [1] although it had been known for several years that 3- to 6-fold synangia with different types of symmetry are rather common at the classical maggot fern site [2]. Synangia with different number and symmetry are usually found on the same pinnule (Fig. 1-3), and it can be assumed that 3-to 6-fold ones could be found on the same frond. Very rarely a 2-fold one is seen beside 3- and 4-fold ones, or a 7-fold one beside 5-and 6-fold ones.

Other features of the synangia are more suitable for distinguishing between maggot fern variants: The pedical can be much shorter than wide and thus hardly visible, or it can be rather distinct. The sporangia can be thick and short or narrow and tapering. With the usual random orientation of the pinnules with respect to the cut plane, good sections along the synangium axis are rare but conspicuous cross sections as in Figs. 1-3 are numerous. Incidentally well-done longitudinal sections can be expected, of course, from those rare samples which contain tens of thousands of pinnules [1,3].

						Fig.1: 4-fold synangia in a maggot stone from Kleinnaundorf-Burgk
						Fig.2: 3- to 5-fold synangia in a maggot stone from Kleinnaundorf-Burgk
						Fig.3: 4- to 6-fold synangia in a maggot stone from Kleinnaundorf-Burgk

Hairs on the sporangia are well known from Scolecopteris species found in "coal balls" in North America but have been found in the Doehlen basin in only two samples so far. An evaluation of the more useful but rare or elusive features of the synangia in the cherts of the Doehlen basin has not yet been done.

text: H.-J. WEISS/Rabenau, photographs: H. SAHM/Dresden