Zosterophyllum fertile, Leclercq, 1942

McSweeney, Fearghus R., Shimeta, Jeff & Buckeridge, John St J. S., 2022, Lower Devonian Zosterophyllum-like plants from central Victoria, Australia, and their significance, Memoirs of Museum Victoria 81, pp. 25-41 : 28-29

cf. Zosterophyllum fertile Leclercq, 1942

Figure 3a–c

Material examined. NMV P50040.1 and P50040.2, part and counterpart, respectively.

Locality. Occurs on a road cutting on Frenchmans Spur Track, approximately midway between Big River Road to the northnorth-west, Warburton Road to the east and Frenchmans Spur Track, ∼ 10 km west of Matlock , central Victoria .

Horizon and age. Wilson Creek Shale Formation, middle Pragian–Emsian, Lower Devonian ( Carey and Bolger, 1995; Mawson and Talent, 1994).

Description. The specimen consists of part and counterpart of one partial spike with basal and apical regions missing and preserved as a carbonised compression. The axis is ∼ 1.0 mm wide and 10.0 mm long and unbranched, and the spike up to 6.8 mm wide. Eight sporangia are borne alternately in two rows. The sporangia are attached by recurved stalks; some are perpendicular to ∼ 60° to the fertile axis and curve sharply distally to at most 90°. The convex margins of some of the sporangia possess a thickened/darker/border, here interpreted as likely pertaining to dehiscence (fig. 3, sporangia 6, 7). An adaxially orientated basal lobe occurs on some sporangia (fig. 3b, central arrows).

Remarks. The sporangia are in two rows with no clear demarcation between the attachment of the stalk and the basal region of the sporangia. The specimen bears some resemblance to Edwards’ (1969a: fig. 1b) South Wales Z. cf. fertile . Edwards’ (1969a) specimens are from the Old Red Sandstone Brecon Beacons and Llanover Quarries, South Wales (Pragian–Emsian Lower Devonian age) and were placed in Z. cf. fertile , because the original diagnosis was based on only a single specimen from Belgium ( Leclercq, 1942) such that further specimens from both Wales and Belgium were thought necessary to determine specific affinity with confidence. Wellman et al. (2000) recorded the earliest occurrence of Z. cf. fertile from the Anglo-Welsh Basin as being mid-Lochkovian (Lower Devonian). The fructification of Edwards’ (1969a) specimens, while incomplete, were 1.0 cm high and 3.0 mm wide, which is comparable in height but over two times smaller than the Victorian specimen, which reached 6.8 mm wide. Edwards’ (1972) Z. fertile , also based on an incomplete spike but with a significant proportion preserved, was 7.2 cm high and 3.0 mm wide, while Wellman et al.’s (2000) Z. cf. fertile reached 2.0 cm in height and 3.5 mm wide. Axial width for Leclercq’s (1942) holotype measured 1.0– 1.5 mm wide and conforms to the Victorian specimen. However, the Victorian specimen’s axis, where visible, was found to be ~1.0 mm wide. The widest axial width for Z. fertile was found by Edwards (1972: 78) for a specimen from the Lower Old Red Sandstone of Forfar, Scotland, with an axial width of 3.0 mm, decreasing only slightly to 2.8 mm wide, while the specimens of Z. cf. fertile from Brecon Beacons Quarry, according to Edwards (1969a: 924), showed greater range, 0.8–2.5 mm wide.

The stalks for Leclercq (1942), Edwards (1969a, 1972) and Wellman et al. (2000) range between 0.3–0.5 mm wide and 1.0– 1.8 mm long. The Victorian cf. Z. fertile stalks are broadly similar, 0.5–0.7 mm wide and up to ∼ 2.0 mm long.

The sporangial shape in face view for the Victorian specimen is reniform (fig. 3, sporangium 8), similar to Wellman et al. (2000), while Leclercq (1942) described it as elongate– reniform, and Edwards (1969a) for Z. cf. fertile described it as irregular. The sporangia examined by Leclercq (1942), Edwards (1969a, 1972) and Wellman et al. (2000) were all in the range of 2.0– 2.5 mm wide and 1.6–3.1 mm high. The sporangial dimensions of cf. Z. fertile are difficult to ascertain due to their poor preservation.

Edwards (1969a: 924) found the longest fructification of Z. cf. fertile . It had eight sporangia but lacked an apical region. Due to the lack of a complete spike herein and poor preservation resulting in equivocal characters, the Victorian specimen was placed in cf. Z. fertile , it being conceivable that given better preservation the plant might be placed it outside the defining characteristics of Zosterophyllum .

Figures

Figure 3. cf. Z. fertile, from the Wilson Creek Shale Formation on Frenchmans Spur, 10 km west of Matlock: a, part (NMV P50040.1); b, line drawing of partial spike. Abx = abaxial valve, Adx = adaxial valve, Q =?poorly preserved sporangium, P = stalk, which is normal to the fertile axis before turning upwards. Central arrows pointing to lobes; c, counterpart (NMV P50040.2). Note. Counterpart image reversed to be in the same orientation as the part.