Stems are slender with a helical leaf arrangement. They are always fragmentary, but the longest fragment is 360 mm. The leaves are inserted at a perpendicular angle or even at a downward angle, after which the leaf departs at an acute angle thus commonly forming a pouch (Fig. 2).

Figure 2. 

Side view of leaf attachment: sample 191, Mt Pelé. (Arrow indicates leaf attachment).

The 85 measurements of the stem width indicate a diameter of 2 to 36 mm (mean 11 mm). Samples from the Mont Pelé are the smallest (on average 10 mm), while samples from Lubná, Oelsnitz and Ronchamp have on average wider stems (mean respectively 13, 16 and 17 mm).

Leaf cushion length varies between 3 and 22 mm (mean 7 mm). Samples from Oelsnitz, Ronchamp and Lubná display longer leaf cushions (mean respectively 8, 9 and 12 mm). Leaf cushions are between 1.3 and 6.7 times longer than wide (mean 3.5, indicating an average width of 2 mm). The Oelsnitz samples have relatively broad leaf cushions (on average only 2.3 × longer than wide).

The scar position in the present data determines the length of the basal and apical leaf cushion field (Fig. 1). On average the 20 % of the total leaf cushion length represented by the leaf scar is in the lower half of the leaf cushion, thus leaving 35% for the basal leaf cushion and 45% for the apical one. In plotting the size of the basal field relative to the total leaf cushion length against the relative size of the apical field to the total leaf cushion length (Fig. 3), it becomes apparent that the Lubná and two Ronchamp samples have a relatively large basal leaf cushion field (Fig. 4A), while the Mt Pelé, Oelsnitz and Kladno specimens have a small basal field and a relatively large apical field (Fig. 4B).

Figure 3. 

Diagram of the relative dominance of the basal over the apical leaf cushion field. Legend: Horizontal axis: Length apical leaf cushion field/ total length leaf cushion, vertical axis length basal leaf cushion field/ total length leaf cushion. Pink square: Lubná red cross: Mt Pelé, light green diamond: Ronchamp, dark green cross: Oelsnitz, dark blue star: St Etienne, purper circle: Kladno.

Figure 4. 

Variations in leaf cushion organisation: A Leaf cushion organisation in a specimen with a relatively dominant basal leaf cushion field, Sample E 06944, Lubná B Leaf cushion organisation in a specimen with relatively dominant apical leaf cushion field, Specimen 223, Mt Pelé.

Leaf scars are broader than height. The leaf scar is apically rhombic acute, basally rhombic obtuse, with a height of 1-3 (mean 1.5) mm and a width of 1–3.5 (mean 2) mm.

The average leaf scar density varies strongly between 1 and 34/cm² (mean 9/cm²). Scar density in the Mont Pelé material is highest (10/cm²), and is lower for the Lubná, Ronchamp and Oelsnitz samples (mean respectively 3, 3 and 7/cm ²). Furthermore, as can be inferred from the scar density plotted against stem width, these properties are correlated (Fig. 5A). The scar density decreases with the increase of the stem width. At the same time leaf cushion length and width increase with stem width (Fig. 5B,C).

Figure 5. 

Changing properties with changing stem width: A Diagram of the scar density (in n/cm²) to the stem width (in mm) B Diagram of leaf cushion length (in mm) to stem width (in mm) C Diagram of leaf cushion width (in mm) to stem width (in mm).

The angle of bifurcation in leaf specimens ranged from 2 to 41 degrees for the first bifurcation, and 18 to 68 degrees for the second. The second angle is generally larger than the first (Fig. 6A).

Figure 6. 

Leaf structures: A Leaf displaying two consecutive bifurcation angles, the second angle is larger than the first, sample 30, Ronchamp B Stomatal furrows as pronounced protrusions on the adaxial side of the leaf surface, note several thin striae between the furrows, sample 220 Mt Pelé C Stomatal furrows as pronounced depressions on the abaxial side of the leaf surface, note the midvein depression, sample 225 Mt Pelé D Venation in a Dicranophyllum gallicum leaf, note the trajectory of the midvein from the inner edge of the second leaf segment, gradually back to the centre position before the second bifurcation, sample 157, Mt Pelé.

As most leaves were incomplete, only the length of the middle segment could be measured. The length of the middle leaf segment varied between 1.4 and 87.0 mm (mean 18.2). The Mont Pelé samples had the smallest middle segment (mean of 8.4 mm), while Ronchamp, Lubná and Sperberbach second leaf fragments were larger (mean respectively 15.7, 19.7 and 19.9 mm).

The width of all three leaf fragments could be measured varying between 1.0 and 4.6 mm (mean 2.3 mm). While the width of the first non-bifurcated segment of Mt Pelé samples was relatively small (mean 1.9 mm), those of Ronchamp, Lubná and Sperberbach was relatively large (mean respectively 2.1, 2.9 and 2.9 mm). The width of the second segment varied between 0.6 and 2.5 mm (mean 1.4 mm) while, again, the width of the second segment of Mt Pelé samples was relatively small (mean 1 mm), and that of Ronchamp, Sperberbach and Lubná samples was relatively large (mean respectively 1.3, 1.8 and 2.0 mm). Finally the same was the case for the width of the third segment that varied between 0 and 2.1 mm (mean 0.5 mm). While the width of the third segment of the Mt Pelé samples was smallest (mean 0.2 mm), that of Ronchamp, Sperberbach and Lubná samples was relatively large (mean respectively 0.5, 0.9 and 1.4 mm).

Two rather distinct cuticular patterns on D. gallicum leaves can be observed on the different sides of the leaf. In a few specimens, two furrows were very clearly pronounced as protrusions on the impressed surface and no midvein was apparent (Fig. 6B); instead, we observed several thin striae between the furrows. As the furrows are documented to be located on the abaxial side of the leaf (Barthel 1977, Meyen and Smoller 1986), these leaves are identified as impressions of the abaxial side of the leaf. Impressions of the adaxial side of the leaf form the second leaf pattern that consists of a narrow midvein intrusion and two wide depressions which indicate the location of the underlying furrows pushing the adaxial leaf surface upwards (Fig. 6C). The furrows are between 0.3 and 0.4 mm (mean 0.35 mm). After its first bifurcation the midvein was observed to follow a distinct trajectory into the second leaf segment (Fig. 6D). It splits some distance before the actual bifurcation of the leaf and then follows the inner edge of the second segment while gradually returning to the centre position in the leaf sheet. Simultaneously, a new furrow appears alongside it.

Based on present observations of the adaxial and abaxial sides of the leaves of D. gallicum (Fig. 6B, C), it was possible to reconstruct the cross section of the leaf (Fig. 7A, B). As the furrows are visible on both sides of the leaf, the leaf of D. gallicum is expected to have been rather thin. The furrows on the underside of the leaf push the upper leaf surface upwards, causing the depressions in impressions of the adaxial leaf surface.

Figure 7. 

Diagram of leaf structure: A Reconstruction of the adaxial leaf side of Dicranophyllum gallicum, note the path of the midvein in the second segment of the leaf B Reconstruction of the abaxial leaf side of Dicranophyllum gallicum, note the prominent furrows and the absence of a clear midvein.

On some compression fossils marginal microdenticulation is preserved (Fig. 8A).

Figure 8. 

Leaf details: A Marginal microdenticulation, sample 34, Ronchamp (arrows indicate microdenticulation). B. Basal part of the leaf showing that the two stomatal furrows do not run all the way down in the leaf base, sample 1529, Mt Pelé (arrow indicates origin of furrow).

Reconstructing the attachment of leaves to the stem is difficult, as these two organs are commonly found separated from each other. Several specimens of D. gallicum do show a stem fragment with remnants of attached leaves, in which the leaf follows a specific curve as it escapes from the stem. There is little information on how this trajectory appears on leaf remains, as most leaves with clear venation are broken off and left their basal portion behind. An exception was found on specimen 1529 of Mt Pelé (Fig. 8B): this is an impression of the abaxial side of a leaf. The basal part of the leaf shows that the two furrows do not run all the way down in the leaf base, but find their origin more centrally to the leaf scar. Extrapolation of the orientation of the two furrows relative to the midvein indicates an origin for the two furrows near the basal portion of the leaf scar.

Well-preserved axillary shoots were found in the collections of the Museum of Natural History in Prague. Various shoots are attached to the stem of Dicranophyllum gallicum specimens from the Lubná locality (Fig. 9A-D). They are composed of elongated scales of 6 mm in length and 2 mm in width and are commonly positioned in the leaf axil. Although they have a general conical shape, their apical end is often widened (Fig. 9A). Their length varies between 4.0 and 14.0 mm (mean 8.0 mm), and their width varies between 2.5 and 7.0 mm (mean 4.0 mm) (Suppl. material 4). A cross section of one of these structures (Fig. 9D) could also be observed. It clearly displays the helical arrangement of the scales forming it. Some specimens from the Mont-Pelé locality also show axillary shoots.

Figure 9. 

Axillary shoots: A Axillary shoot with apical widening (indicated by arrow), E 06946, Lubná B Axillary shoot with subtending leaf (indicated by arrow), sample E 06946, Lubná C Axillary shoot without broad apical widening, sample E 06950, Lubná D Cross section of axillary shoot, sample E 06946, Lubná.

A total of 15 seeds was observed on the specimens in our study (Supplementary File 5). They were found dispersed on specimens from the Mont-Pelé locality, with one exception from the Ronchamp locality (specimen 1362). Seeds have a conical to ovate shape, 2.6-3.8 mm long (mean 3.4 mm) and 2.8-3.8 mm wide (mean 3.1 mm), usually longer than wide. A nucellus can often be observed and is 1.0-1.5 mm long (mean 1.2 mm) and 0.7-1.2 mm wide (mean 1.0 mm). The seed base is rounded, the chalaza part is flattened to notched or cordate (Fig. 10A). The seed surface is striate (Fig. 10B). The apex is notched with what appears to be a (sometimes wide) micropyle (Fig. 10C). In a single seed (Fig. 10B) a triangular cavity which could be interpreted as a pollen chamber is seen in the seed. The integumentary coat is thick (200 µm), apically slightly thicker than basally. Two seeds are positioned next to a Dicranophyllum gallicum leaf, one of which shows an organic bridge between the leaf and the seed, but the bridge is interrupted (see Fig. 10D).

Figure 10. 

Seeds: A Seed with notched chalaza, sample 1529, Mt Pelé B Striate seed with visible pollen chamber, sample 75, Mt Pelé C Seed with visible micropyle, sample 75, Mt Pelé D Seed possibly on first leaf segment, sample 1362, Ronchamp (arrow indicates interrupted organic bridge).

The stem diameter recorded in the literature hovers around the mean values of 11 mm recorded here such as 9.0 mm for D. gallicum var. parchemineyi (Renault and Zeiller 1888), 10 mm for the German D. gallicum described by Barthel (1977) and 8 to 14 mm for the 7 samples from La Magdalena (Castro Martínez, 2005). Samples from Lubná, Oelsnitz and Ronchamp are wider, sample 10472 from Ronchamp being 36 mm wide. This indicates that the variability in the present European stem selection is much higher than what was recorded until now.

Leaves were found attached to stems of various sizes, implying that the plant had leaves covering most of the stem. Nonetheless, stem 221 in our study material shows a transition from large, well-developed leaf cushions to small, poorly defined leaf cushions. This transition gives an indication that the more apical part of these stems was still developing, while the more basal part was mature. Periodic growth patterns have not been observed on any stems, not even on the longest stem fragments of D. gallicum. This suggests that stem growth in D. gallicum never halted, that is, it was more or less continuous.

Many stem fragments are gently curved. Although we have not analysed this character in detail, it makes sense to expect that thicker stems are more resistant to bending, while slender stems are more flexible (also being younger). The majority of stems in the Dicranophyllum gallicum material is slender and curved to some extent, indicating that during its life the plant was probably flexible.

Grand’Eury (1877), Renault and Zeiller (1888) and Barthel (1977) considered the leaves to be persistent. The density of attached leaves appears to have been the largest in the apical regions, where establishing the details of the leaf morphology was often difficult as the leaves were preserved on top of each other. In the present material specimens with thick stems still had leaves attached (e.g. specimen 223), while other stems were completely devoid of leaves, suggesting leaf persistence related to an ecological factor.

Leaf cushion length and width from literature, respectively 4-7 mm and 2-3 mm (Zeiller 1880, Renault and Zeiller 1888, Castro Martínez 2005), is shorter than the mean values found in the data set described here (respectively 7 to 2 mm). However, it has been said to vary considerably (Renault and Zeiller 1888, Barthel 1977).

The dominant leaf cushion organisation with a large apical field is in contrast with the leaf cushion organisation given in Grand’Eury (1877). He described the leaf scar as positioned in the upper third of the leaf cushion, thus resulting in a very small apical field. Renault and Zeiller (1888) even placed the leaf scar in the upper quarter of the leaf cushion. Scrutiny of the illustrations of Grand’Eury (1877, plate XIV, fig 10, in particular) confirms a position of the leaf scar in the upper half of the leaf cushion, yet in Zeiller (1880, plate CLXXVI, fig 1) it cannot be established. In Renault and Zeiller (1888, plate LXX, fig 8 and plate LXXI, fig. 5), on the contrary, the scar is illustrated as either positioned basally or centrally in a similar way as for the bulk of the collections described herein.

As only the Lubná and the two Ronchamp samples have a well-developed basal leaf cushion field, these specimens are best comparable to the figured paratype of Grand’Eury (1877, plate XIV, fig 10). This is in contrast with the samples from Mt Pelé where, inversely, the apical field dominates over the basal field.

Renault and Zeiller (1888) described the angle of leaf bifurcation as 30° for the first bifurcation and 40° for the second. Barthel (1977) reported angles between 6° and 30°. The variation in angle size for the material described herein is much wider (2° to 68°) than what is given in the literature, yet the first angle is, indeed, commonly smaller than the second.

Earlier Dicranophyllum gallicum descriptions indicate that the total leaf length varied between 33 and 60 mm, with on average 15-20 mm for the first segment, 10-15 mm for the second and 8 to 10 mm for the third (Zeiller 1880, Renault and Zeiller 1888, Barthel 1977, Castro Martínez 2005). Doubinger et al. (1995) considered that the leaves can reach a length of 200 mm. The present material, based on our measurements of the second segment (mean 18.2 mm), was slightly larger than what was described earlier. Lubná, Sperberbach, Manebach and Ronchamp leaves were even larger (on average respectively 20, 17, 20 and 16 mm), while the Mt Pelé samples were, again, relatively small (8 mm).

The leaf width from earlier studies varied between 1.5 and 2.0 mm (Renault and Zeiller 1888) or between 2.0 and 3.0 mm (Barthel 1977). In the present material the leaf width varies between the same values.

Dicranophyllum gallicum found in the Erzgebirge has small abaxial stomatal furrows of 0.2 to 0.25 mm wide. The furrow width in the present material was slightly larger (0.35 mm). Thin striae as found here between the two furrows have also been described earlier as five strong lineations in D. gallicum samples from the Goldlauterer Schichten (Barthel 1977).

The trajectory of the midvein presented above (Figs 6, 7) is one where the midvein approaches the leaf margin at the leaf bifurcation, to later diverge from the leaf margin and to again reach the central part of the leaf. This midvein pattern was not described earlier and is depicted differently in Barthel (1977) as splitting a few millimetres from the leaf margin in such a way that the two new veins always remain central to the leaf.

Barthel (1977) describes a process of leaf development as starting with simple unbifurcated leaves, after which the leaves produce a first, terminal bifurcation and, finally, a second bifurcation. According to De Lima (1888) a leaf can bifurcate three times.

Based on present material it is difficult to conceive such a leaf development, as no clear simple leaves on any D. gallicum specimen was observed. Incomplete leaves without bifurcations were observed, these could be associated to D. gallicum based on venation properties, that is, the clear presence of furrows, but it was not possible to make statements about whether those leaves bifurcate or are, indeed, simple leaves. A few leaves do display a size and shape that suggests an early stage of development (Fig. 11), but these already have two bifurcations. Ultimately, our material provides too little evidence to make an assumption about how the leaves developed.

Figure 11. 

Possible juvenile leaf, sample 28, Mt Pelé.

Renault and Zeiller (1888), in describing a sample from Puits Forêt, indicated a charcoalified body formed by scales of 5 to 6 mm long and 2 to 3 mm wide attached to the stem. These scales are comparable in size to the scales described from the axillary shoots described above. Renault and Zeiller (1888) described the charcoalified body as seemingly forming a bud that had contained microsporangia, while the whole shoot was reminiscent in shape and size to cordaite male organs.

Dicranophyllum hallei also displays axillary shoots and Barthel and Noll (1999) suggested that these represent fertile cones (either male or female) while Noll (2011) found a dispersed female cone of D. hallei. In Barthelia furcata axillary shoots subtended by a forked bract represent ovuliferous dwarf shoots (Rothwell et al. 2005). In Anderson et al. (2007, fig. 2, p. 114), axillary shoots of Dicranophyllum gallicum are described as male cones, but in Meyen (1987) the axillary shoots, compared to axillary buds in Mostotchkia, are said to have been misinterpreted as microstrobili. From the present material and from what was described earlier, no unequivocal proof of the true nature of these axillary structures can be deducted.

Seeds were already mentioned by Grand’Eury (1877) as very small, conical shapes positioned just above rather than at the leaf axil. Seeds have been found attached to the first leaf segment for Dicranophyllum gallicum var. parchemineyi, and described to be 4 mm long and 3 mm wide (Renault and Zeiller 1888). These sizes differ slightly from what is observed in present material (on average 3.4 long and 3.1 wide), but certainly are in the same order of magnitude. The nucellus described in the results above is smaller (mean 1.2 long and 1.0 mm wide) than what is described in Renault and Zeiller (1888) that is, 2.8 to 2.0 mm. The integumental coat, while being apically thicker in a similar way to what was described earlier, does not reach the 1 mm indicated in Renault and Zeiller (1888). These differences in size can be hypothesized to relate to the Mt Pelé material being generally smaller than was described earlier. On the other hand, because seeds are propagules and conical seeds with a nucellus and a pollen chamber are produced by numerous divergent taxa, the occurrence of these seeds in both the Ronchamp and the Mt Pelé samples and their resemblance to the seeds described by Grand’Eury (1877) and Renault and Zeiller (1888) have to be considered here as probably coincidental and further advances on Dicranophyllum gallicum will have to await new and better finds.

Obviously, finding and describing the original material of Dicranophyllum gallicum Renault & Zeiller, 1888, would give unequivocal proof of the nature and organisation of the female fertile structures, but, in spite of a specific search for it, this sample cannot be located. Here we only have the interrupted organic bridge between the leaf base and the seed (Fig. 10D). As D. gallicum var. parchemineyi was illustrated with its seeds attached to the first, non-bifurcated segment of the leaf (Renault and Zeiller 1888, plate LXXI, fig. 5), it is tempting to consider this seed to be attached to the leaf as well, given its proximity and orientation towards the leaf. However, it is not possible to find stronger evidence for any further physical connection between the leaf and seed.

As seen in the results, the Mt Pelé samples are relatively small in leaf and stem size, have a normal leaf cushion length, have the highest leaf scar density and have a dominance of the apical over the basal leaf cushion field. The Lubná, Ronchamp and Oelsnitz samples, in contrast, relatively have a large stem and a short leaf cushion with a large basal leaf field and low scar density.

Such differences in features could indicate a phylogenetic differentiation, where the large Lubná samples are ancestral to smaller Dicranophyllum gallicum specimens, Lubná is amongst the oldest (from the Westphalian C, Table 1) localities in the present series, yet the D. gallicum from Kladno originates from the same Radnice Member as the Lubná samples do, yet ranges with its smaller dimensions and leaf cushion organisation with the rest of the French and German D. gallicum. It was demonstrated that scar density was negatively correlated to stem width (Fig. 5A), while leaf cushion length and width correlates positively to stem width (Fig. 5B, C). Lubná samples, have relatively large stems, low scar density and long and wide leaf cushions and are considered to have represented matured plants, having had the time to grow thicker stems, and longer and wider leaf cushions, thus resulting in a reduced scar density. The relative dominance of the basal over the apical leaf cushion field (Fig. 3), typifying the Luba specimens, consequently is hypothesized here to relate to an ontogenetic development. The paratype (Grand’Eury 1877, plate VIV, fig. 10), the samples from Lubná and two samples from Ronchamp are considered to have been more mature specimen, while the Mt Pelé samples, with thin stems, relatively elongated leaf cushions and a high leaf scar density, are considered juvenile forms. As there is no systematic relation between lithology (Table 1), considered here as a reflection of the environmental setting, and specimen dimensions, ecology is not considered to play a part in the variability described herein.

For the reconstruction of the habit of Dicranophyllum gallicum using Niklas' (1994) method, only the diameter of the plant is required. By using this method it has to be assumed that D. gallicum was a self-supporting plant, as the method was shown to be inapplicable to liana species (Niklas 1994, p. 1237). Indeed, D. gallicum shows no features like climbing hooks (see, for example, Krings and Kerp 1999 or Krings et al. 2003a).

In spite of Grand’Eury’s (1877) early suggestion that a woody body formed underneath the leaf cushions and Barthel's (1977) description of Dicranophyllum gallicum as a woody plant, there is some uncertainty as to the true woodiness of the stem. Assuming that D. gallicum was, indeed, a woody plant and taking the largest stem diameters of 36 mm, it is calculated to have reached a height of at least 4.5 m (Table 2).

This expected height could increase if D. gallicum were shown to have branched. Grand’Eury showed a single specimen with a branching stem fragment (Grand’Eury 1877, plate XIV, fig. 8), and reconstructed the species accordingly as a small tree (1877, tableau de vegetation D, bottom left). However, no other D. gallicum fossils showing branching have been found since and none of the specimens in our study showed branching; Grand’Eury (1877) figured specimen with a bifurcating branch is the only one showing this feature. This indicates that branching is either a rare occurrence in D. gallicum or the plant did not branch at all, thus suggesting that the specimen from Grand’Eury (1877) would be of a different species. For our reconstruction of D. gallicum, we propose that the plant had a simple, unbranched stem, which reached 4.5 meters in height (Fig. 12). This is comparable to the reconstruction of Dicranophyllum hallei by Barthel et al. (1998), in which a nearly complete, unbranched shoot of 2 m long is described. The stem widths of D. hallei specimens we observed were usually slightly greater than the D. gallicum measurements, indicating that D. hallei grew taller than D. gallicum.

Figure 12. 

Reconstruction of Dicranophyllum gallicum.

Finding similarities between the pollination and fertilization process, and the presence of the retained motile sperms in Ginkgo and the Cycadales, Thomas and Spicer (1987) suggested the existence of a group of primitive pteridosperms for the common ancestor of the later. Such a group of primitive pteridosperms holding Dicranophyllum gallicum supports the views of Archangelsky and Cúneo (1990) of the Dicranophyllales representing an order of primitive gymnosperms. Rothwell et al. (2005) in their study of Hanskerpia found Dicranophyllum hallei to be positioned between the Cordaitales and the Voltziales at the base of the early conifers. Given that Renault and Zeiller (1888) considered Dicranophyllum gallicum to possibly have had male axillary shoots reminiscent of the microstrobili in Cordaitales, such a position for a member of the Dicranophyllales at the very base of the early conifers would be corroborated by an interpretation of the present axillary shoots as pollen cones, but in the absence of any unequivoval proof of them representing pollen cones, the axillary shoots are considered here as vegetative buds. As such this interpretation does not differ from the description given in Rothwell and Mapes (2001). They described D. gallicum as being represented by female fertile structures only and they considered it challenging to give a systematic assignment to early coniferophytes in general, e.g. the DicranophyllalessensuMeyen (1987).

Marginal microdenticulation

Marginal microdenticulation (Fig. 8B) may indicate adaptation to a xeric environment, in which the teeth aid the plant in maintaining its internal temperature or absorb nutrients, as found in some extant xerophilic species (e.g. Benzing 1976, Benzing et al. 1976). However, marginal teeth are known to serve different functions for plants such as defence against herbivory (Krings et al. 2003b) and storage of minerals (Broadhurst et al. 2004).

Stomatal furrow

Although it was not possible with the present material to perform a cuticular analysis on the leaves of Dicranophyllum gallicum, Barthels' (1977) work shows that the stomata of this species occur in the embedded abaxial furrows. Jordan et al. (2008) showed that encryption of stomata in grooves (as found in Dicranophyllum) has evolved separately several times in a number of species of Proteaceae that are known from arid to semi-arid environments. Archangelsky et al. (1995) associated the hypostomatic leaves of the Cretaceous cycad Pseudoctenis ornata Archangelsky to the volcanic environment in which it occurred. The hypostomatic nature of the leaves provides no certainty about the vegetation density, which may be open as well as closed (Jordan et al. 2014). Moreover, Parkhurst (1978) explained that stomatal distribution is not primarily caused by environmental factors, but can be seen as an indicator of leaf thickness (thick leaves generally being amphistomatous).

Other plant fossils found co-occurring on the Dicranophyllum gallicum samples

Information about associated plant species occurring beside Dicranophyllum gallicum mainly comes from the tuffaceous material of the Mont-Pelé locality. The specimens from this locality had fragments of Calamites, Pecopteris, Nemejcopteris, Alethopteris, Neuropteris, Sphenopteris, Cordaites, and the seeds Pachytesta and Samaropsis associated with them. Also, on specimen E 06948 from the Lubná locality, a megasporangium of an Omphalophloios sp. was found. These genera are predominately known from the late Pennsylvanian tropical forests of Euramerica and, as Dicranophyllum gallicum was maximally 4.5 m high, it is suggested here that the plant stood in the shade of its taller associates. Omphalophloios feistmantelii is also 2-3 m in height and has been interpreted as a plant able to rapidly colonize local habitats, preferring peat and mixed peat-clastic swamps (Bek et al. 2015). Dicranophyllum gallicum, because of its comparable size and co-occurrence, is suggested here to have occupied the same or similar habitat.

Sediment

Dicranophyllum gallicum is as often preserved in tuffs as in shales (Table 1). Assuming the specimens preserved in tuffs are (par-) autochtonous, D. gallicum may have thrived in the mesic-xeric areas from a volcanic slope with active volcanism. The specimens found in shales are considered to have grown in wetter areas, as suggested in Anderson et al. (2007) for Dicranophyllaceae, in riparian or lake-side environments. Yet the occurrence in tuffs supports a more ruderal behaviour that the association with an Omphalophloios sp. already suggests, thus indicating an opportunistic colonization strategy. According to Wagner (2005) the paucity of Dicranophyllum finds may have indicated that it had ecological requirements differed from those prevailing in the ‘'coal measures' and rather belonged to extra basinal, well-drained soils. Considering D. gallicum is found both in shales and in tuff, an opportunistic colonization strategy as for Omphalophloios sp. is preferred here.