Phlebopteris sp.

Pott, Christian, 2014, The Upper Triassic flora of Svalbard, Acta Palaeontologica Polonica 59 (3), pp. 709-740 : 720

Phlebopteris sp. cf. Phlebopteris muensteri (Schenk, 1867) Hirmer and Hörhammer, 1936

Fig. 4H.

1972 cf. Thaumatopteris brauniana Popp ; Vasilevskaya 1972: 40, pls. 4: 4, 5; 5: 4, 5.

Material.— Spitsbergen: Bertilryggen (NRM S080257); Wimanfjellet (VSEGEI 10979-31–10979-33, 10979-87– 10979-89); Carnian (Upper Triassic).

Description.— The specimens assigned to Phlebopteris are all fragmentary and most are sterile portions from the middle of a large frond (Fig. 4H 1). The largest is 134 mm long with pinnules up to 77 mm long. The densely spaced pinnae are inserted laterally by their whole width to a prominent rachis that is typically 4 mm wide. Pinnules are 5–8 mm wide and taper gradually towards an acutely rounded apex. They are characterised by a prominent, 1 mm wide midrib emerging at an angle of 75–85° from the rachis; secondary veins are barely visible in the fossils. At least two specimens from Wimanfjellet appear to bear sori in a row along the midvein of the pinnules (Fig. 4H 2). The specimens from Bertilryggen probably constitute more apical portions; pinnules in these are inserted at angles of 50–55° and decrease in length towards the apex.

Remarks.— The fossils match closely specimens assigned to Phlebopteris muensteri (cf. Hirmer and Hörhammer 1936; Schweitzer et al. 2009; Pott and McLoughlin 2011). The secondary veins, including the mesh-like pattern crucial for a definite assignment, are barely visible in all specimens from Svalbard. However, some specimens bear an indistinct row of sporangia flanking the pinnule midvein, which is a characteristic feature of Phlebopteris . Sporangia in the very similar Thaumatopteris brauniana Popp, 1863 are distributed among the veins over the whole abaxial surface of the pinnules. The straight margin of the pinnules also favours assignment to Phlebopteris whereas pinnule margins in Thaumatopteris are usually undulate/lobate. The differences in venation separating these genera are not visible in the Svalbard specimens. Moreover, Phlebopteris is a typical fern of the Carnian, whereas Thaumatopteris becomes common only in the Rhaetian. Specimens identified by Vasilevskaya (1972) as cf. Thaumatopteris brauniana are here transferred to Phlebopteris . However, since venation details are absent from the Svalbard specimens, assignment to species level is with some reservation.

Geographic and stratigraphic range.— Europe, Middle East; Carnian–Lower Cretaceous.