Salopella Edwards and Richardson, 1974

McSweeney, Fearghus R., Shimeta, Jeff & Buckeridge, John St J. S., 2021, Early land plants from the Lower Devonian of central Victoria, Australia, including a new species of Salopella, Memoirs of Museum Victoria 80, pp. 193-205 : 195-196

Genus. Salopella Edwards and Richardson, 1974

Type Species. Salopella allenii Edwards and Richardson, 1974

Salopella australis Tims and Chambers, 1984 ( fig. 2A–G ; line-drawing fig. 6A )

Salopella australis Tims and Chambers (1984 : pl. 32, figs. 1–6 ; pl. 34, figs. 4 , 5 ; text-fig. 2A–C)

Emended diagnosis (after Tims and Chambers, 1984). New information in bold. Axes 0.9–2.4 mm wide with central line, at least two long aligned parallel parent axes with one dichotomy each resulting in narrower shorter daughter axes terminated by a single sporangium on each. Plant at least 80 mm high. No obvious branching at the base of the sporangia. Sporangia 6.5–14.0 mm high and 1.3–2.0 mm wide, with parallel sides in the lower two-thirds of the presumed fertile portion. Sterile sporangia apex tapering to a point in the upper third. Spore characters unknown.

Locality. Frenchmans Spur Track, 10 km west of Matlock , Victoria. 37° 25.82' S , 146° 77.24' E.

Stratigraphy and age. Wilson Creek Shale, mid-Pragian– Emsian, Lower Devonian ( Carey and Bolger, 1995; Mawson and Talent, 1994).

Note: Two specimens assigned to S. australis by Tims and Chambers (1984) from Limestone Road have been transferred to Gen. et sp. indet. because the specimens are too poorly preserved to unequivocally assign to any taxon. These are NMV P229617 and NMV P157323; NMV P157323 (Jack Douglas Private Collection) was figured by Tims and Chambers (1984: pl. 32, figs 5 , 6 and text-fig. 2b) but possesses a completely different branching architecture to the holotype for S. australis and has poorly defined sporangia. Specimen NMV P157323 has been re-drawn here ( fig. 6B ) for comparison to S. australis ( fig. 2A–E ). Specimen NMV P50011 from Limestone Road has been moved out of S. australis to a new Salopella species (see below). Most specimens assigned to the Wilson Creek Shale by Tims and Chambers (1984) on Frenchmans Spur track are considered S. australis because they have subtending axes the same width as their sporangia (e.g. NMV P50014, NMV P33219 and NMV P50008 [holotype]). Only in cases where this character is equivocal are specimens assigned to Gen. et sp. nov. (e.g. NMV P50010).

Description. Salopella australis possessed an erect habit with at least two long parent axes aligned parallel to each other and with one distal dichotomy on each resulting in narrower shorter daughter axes, each terminating in an elongate sporangium with an acuminate apex. A slight indentation occurs on some sporangia at the darker carbonaceous area and sterile interface, and proximally the dark carbonaceous area tapers inwards on the daughter axes.

Remarks. A reassessment of the morphospecies Salopella australis as originally determined by Tims and Chambers (1984) has necessitated the removal of some of the specimens attributable to it, primarily due to differing branching architectures and poor preservation. Tims and Chambers (1984: 268) noted four species with two dichotomies, but only three were found; presumably, the fourth is in a private collection. Nonetheless, all the specimens figured in Tims and Chambers (1984) were examined. Tims and Chambers (1984: 270) described S. australis as “open-branched” ( Tims and Chambers, 1984: pl. 32, fig. 5 , 6 ) with at least two dichotomies of widely dichotomising daughter axes emanating from one parent axis, and up to at least 145 mm in length ( fig. 6B ). However, this was found to occur on only three specimens from Limestone Road and was not found on the holotype ( fig. 2D, E – double arrows between aligned parent axes).

The holotype possessed two aligned parent axes, with one of the parent axes dichotomising into shorter narrower daughter axes. The other parent axis was not as well preserved. However, another specimen with better preservation ( fig. 2A, C ) shows both parent axes aligned and dichotomising into shorter narrower daughter axes terminated with elongate sporangia that are no wider than their subtending axes. Tims and Chambers (1984: pl. 32, fig. 4 ) partly illustrated this specimen with only one of the parent axes shown. However, Tims and Chambers (1984) did not mention or show the other parent axis aligned parallel to this axis. Furthermore, there was an additional specimen in the collection not figured by Tims and Chambers (1984), likely due to its poor preservation, but which also had two aligned almost parallel axes and is similar to the holotype with two parent axes aligned and with one of the parent axes possessing a single dichotomy with short daughter axes terminated in elongate sporangia ( fig. 2B ). Even taking into account the effects of degradation of the specimens before fossilisation and the effects of ocean currents on orientation of the axes, the Limestone Road specimens appears to have more in common with S. caespitosa than S. australis , with two dichotomies and relatively longer daughter axes from the ultimate dichotomy ( fig. 6B ).

This emendation has resulted in the maximum known length of S. australis being reduced from 145 mm to 80 mm and the reduction of known dichotomies to one, with the sporangial dimensions and morphology remaining the same. Specimens attributed to S. australis herein ( fig. 2A–E ) were deposited in a deep marine quiescent environment of the Wilson Creek Shale, and like the holotype, possessed parallel erect axes. This branching architecture of erect parallel aligned axes was found only in three specimens, including the holotype. All the other specimens bar one, which is defined below, are too poorly preserved to attribute to any taxon. Parsimony suggests that parallel axes that dichotomise at the same level, with axes of comparable widths, terminating in elongate sporangia on short daughter axes also of equal dimensions, that have been transported a considerable distance belong to the same plant (sensu lato Wang and Hao, 2004; Edwards et al., 2015; Edwards and Li, 2018a) and are representative of its true branching architecture. We acknowledge that we have failed to show organic connection, and current alignment could conceivably result in this axial configuration, but the likelihood of this occurring to three separate specimens with characters such as branching and sporangia occurring at the same height and with the same dimensions is unlikely. We postulate that the parallel aligned axes may have emanated from a rhizomatous region because there was no converging of the parent axes. Two of these parallel aligned specimens were included in Tims and Chambers (1984) but noticeably in both cases, only one of the parent axes was visible (Tims and Chamber, 1984: text-fig. 2A, pl.32, figs. 1 , 2 , 4 ). Additionally, the line-drawing of S. australis in Tims and Chambers (1984: text-fig. 2a) shows the daughter axes of the parent axes with slightly differing lengths, which was based on Tims and Chambers (1984: pl. 32, fig. 1 ). But a closer examination of this specimen (holotype; fig. 2D ) shows the daughter axes are preserved on different levels of lamina, with the perceived shorter daughter axis (upper arrow) partly obscured by another axis.

The specimens removed from Salopella australis ( Tims and Chambers, 1984: pl. 32, figs 3 , 5 ) and placed in Gen. et sp. indet. include isolated poorly preserved sporangia from both the Wilson Creek Shale on Frenchmans Spur ( fig. 2F, G ) and specimens from Limestone Road because the preservations were generally poor and the branching architectures greatly differed to the holotype. One of the excluded specimens ( Tims and Chambers, 1984: pl. 32, fig. 3 ) with differing branching architecture to S. australis is described below as a new morphospecies. Thus, S. australis is no longer represented in the flora of the Lower Plant Horizon.

Figures

Figure 1. Map of Victoria, Australia, showing the fossil locations within the Melbourne Zone. Location 1. Yea, Ghin Ghin Road, Limestone Road (37° 12.38’ S, 145° 25.39’ E). Location 2. Matlock, Frenchmans Spur (37° 25.82’ S, 146° 77.24’ E.), the type location of Salopella australis and S. caespitosa (Tims and Chambers, 1984). Source: adapted from Moore et al. (1998: fig. 2).

Figure 2. Salopella australis displaying parallel parent axes dichotomising into much shorter daughter axes that are terminated with elongate sporangia, delineated with a constriction just above dark sporogeneous region. All from Wilson Creek Shale on Frenchmans Spur track, 10 km west of Matlock.A, erect parent axes parallel to each other, dichotomising into two elongate sporangia from Wilson Creek Shale. Re-photographed here; originally published in Tims and Chambers (1984: pl. 32, fig. 4) and Tims (1980: fig. 4.1.9). Specimen NMV P50014. B, forked dichotomy terminated by sporangia from Wilson Creek Shale. And to the right hand side of the forked axis is another long axis, which based on its orientation may also be part of the same plant. Constriction at arrow, lower arrow at dichotomy and double arrow at two aligned axes. Specimen NMV P33219. C, close-up of fructification in A, sporangia barely extend beyond the confines of their subtending axes, with slight constriction present above sporogeneous region (at arrow). Specimen NMV P50014. D, E, holotype, part and counterpart. On part, constriction at arrow in sporangium. On counterpart, both parent axes are parallel to each other (at dotted arrow). Re-photographed here, originally published in Tims and Chambers (1984: pl. 32, figs. 1, 2). Specimens NMV P50008.1 and NMV P50008.2, respectively. F, Gen. et sp. indet. – short daughter axes terminated in elongate sporangia. The cortex may be absent from subtending axes, with only the central line visible. The lack of cortex prevents assigning to S. australis as width of subtending axis to sporangial width is required. Originally photographed by Tims (1980: fig. 4.1.13). Specimen NMV P50010.2. G, S. australis, with two short daughter axes, with constriction at arrow of the sporangium, which is the same width as its subtending axis. Specimen NMV P202886.

Figure 3. Salopella caespitosa (holotype) from Wilson Creek Shale on Frenchmans Spur track, 10 km west of Matlock. A, B, part (NMV P202987.1) and counterpart (NMV P202987.2), respectively; numbering follows Tims and Chambers (1984, pl. 33, fig. 1). Counterpart images are reversed to be in the same orientation as the part specimen. A, on right-hand side of part specimen, double isotomous dichotomies lead to sporangia one–seven. Note, at the arrows, there is perpendicular branching that is suggestive of a rhizomatous system. C, sporangium 12; at the arrow there is another axis that is terminated in a sporangium that is partially visible. Specimen NMV P202987.1. D–F, Evidence of a slight constriction beneath sporangia at arrows. D, sporangia eight and nine (on the left). Widest part of each sporangium occurring approximately midway along their length. Note, rephotographed; originally published in Tims and Chambers (1984: pl. 34, fig. 3). Specimen NMV P202987.1. E, sporangium 22 is c. 4.06 mm long and 1.4 mm wide. The axis decreases from 1.2 mm proximally to 0.5 mm just beneath the sporangium. Specimen = NMV P202987.2. F, sporangia four (right) and five, both sporangia are slightly wider in the lower quarter of each sporangia. Specimen = NMV P202987.2. G, sporangium 22, appears to be two immature sporangia juxtaposed. At arrow, the apex (rounded) of the smaller fusiform sporangium is apparent. Specimen NMV P202987.1. H, sporangium two, lower arrow at walls surrounding presumed oval sporogeneous area, which reaches approximately halfway the length of the sporangium to the upper arrow. Specimen NMV P202987.1. I, sporangium 13, arrows at walls surrounding sporangeneous area and upper arrow showing extent of oval sporogenous body. The walls does not recombine apically like in sporangium two, suggesting it may have been crushed, or hidden, beneath the matrix. Rephotographed; originally figured by Tims and Chambers (1984: pl. 33, fig. 3). Specimen NMV P202987.2.

Figure 4. Salopella caespitosa NMV P235941 from Devil’s Elbow on Ghin Ghin Road, northwest of Yea. A, overview of whole specimen. NMV P235941.1. B, arrow (Vt) at vascular trace entering base of oval presumed sporogenous body of sporangium four, and the subtending axis to sporangium four pinches slightly about 1 mm below the sporangium. Lower arrow at region where subtending axis is continuous with sporangial wall and upper arrow shows extent of sporangial body of sporangium three. Note, for both sporangia, the distal parts appear to be hidden in the matrix. NMV P235941.2. C, lower arrow (Vt) at vascular trace entering base of oval sporogenous body, with upper arrow at distal extent of sporogenous body on sporangium two on the counterpart. Note, no longitudinally oblique striations are evident in upper half of sporangium but are evident on the part specimen. NMV P235941.2. D, sporangium two at arrow longitudinal oblique striations on the upper half of the sporangium. NMV P235941.1. E, close-up of parent axis with longitudinal striations. NMV P235941.1.

Figure 5. Salopella laidae sp. nov. (holotype) NMV P50011.1 and NMV P50011.2, part and counterpart, respectively, with counterpart reversed to be in the same orientation as part specimen. From location 4 (Brackley’s cutting) on Limestone Road, Yea. A, double isotomous dichotomy visible, terminated with eight elongate sporangia, five visible. At lower arrow central line and at F, folding of tissue. On sporangium seven?sporogenous region highlighted. Rephotographed; originally figured by Tims and Chambers, 1984: pl. 32, fig. 3 and text-fig. 2C. B, arrow at daughter axis missing on part present.

Figure 6. Line-drawings of Victorian early land plants with longer than wider sporangia. A, Salopella australis from Wilson Creek Shale on Frenchmans Spur track, near Matlock. Specimen NMV P50014.B, Gen. et sp. indet. from Limestone Road, Yea. Originally placed in S. australis but branching architecture clearly differs. Specimen NMV P157323. C, Salopella laidae sp. nov. from Limestone Road, Yea. NMV P50011. D, Salopella caespitosa (holotype) from Wilson Creek Shale on Frenchmans Spur track, near Matlock. Specimen NMV P202987. E, Salopella caespitosa from Ghin Ghin Road, Yea. Specimen NMV P235941.