Sphenophyllum  bristle brush
deutsche Version

The ancient horsetail relative [1] Sphenophyllum is well known from its compression fossils in coal bearing formations. With its slender herbaceous body, leaves in whorls, and apparently climbing habit it is surprisingly similar to the flowering plant Galium aparine, the cleavers, a common garden weed.
Sphenophyllum axis Sphenophyllum axisSphenophyllum axis Sphenophyllum axis
Figs.1-4: Sections of the slender climbing axes having one feature in common allocating them to Sphenophyllum.
Height of Figs.2-4: 2mm.
Same scale of Figs.1-5.

Sphenophyllum top section

Sphenophyllum and its close relatives have provided showy pictures in the palaeobotany literature. (Unfortunately, one of the latest publications on the subject [2] is fraught with erroneous size data. Axis diameters, for example, can be less than 1mm as in Fig.4 but never as small as 0.2mm as in [2], Fig.13.)
Crack faces in a sediment with randomly oriented plants may be confusing and less informative but cross-sections of the slender stalks show distinctive shapes which can be recognized as Sphenophyllum, even if slightly tilted or if looking rather different (Figs.1-4). Cross-sections of bristle-like leaves seen nearby (Figs.1,2) also indicate Sphenophyllum.

Fig.5: Seen on the raw surface of a chert boulder from the Permian Döhlen Basin: One Sphenophyllum axis section of the usual type below left and two quite uncommon sections of a brush made of a bunch of bristle-like leaves.
Width of the picture 8mm, same scale as above.

What is seen in Fig.5 has apparently never been pictured before. The structure on the right seems to be a cross-section near the upper end with about 80 bristle-like leaves overtopping the axis and forming a stiff brush, perhaps as a protection for the tip. An even bigger brush section with possibly more than a hundred bristles is less well seen above left,

All pictures have been taken from one chert boulder of 4.7kg found in 2000, labelled Bu7/89. The boulder is a fragment pried loose from a Permian chert layer of about 20cm thickness by the Cretaceous sea, embedded into Cretaceous sandstone, later laid free by weathering, then moved and deposited by a glacial stream. Small remains of Cretaceous sandstone are still adhering to the surface. In this sample, Sphenophyllum is restricted to a layer of a few centimeters. Pinnules of Scolecopteris are scattered throughout. Moult fragments of a small crustacean, probably Uronectes, are also there.
Finally it can be stated that plant fossils preserved in chert, although less conspicuous if looked at from afar, often provide details not seen before.

H.-J. Weiss       2018

[1] A. Elgorriagal, I.H. Escapal, G.W. Rothwell, A.M.F. Tomescu, N.R. Cuneo: ...Evolution of horsetails (Equisetales) within the ... Sphenopsida.  
        Am. J. Botany 105(8): 1–18, 2018.

[2]  M. Barthel: Die Rotliegendflora der Döhlen-Formation. Geologica Saxonica 61 (2) 2015 (2016 released), 105-238.
Scolecopteris pinnule cross-section, Sardinia Permian Chert News 23

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