Arberophyllum substrictum, Pott, 2014

Pott, Christian, 2014, The Upper Triassic flora of Svalbard, Acta Palaeontologica Polonica 59 (3), pp. 709-740 : 732

Arberophyllum substrictum sp. nov.

Figs. 6A, 9H–N.

1972 Glossophyllum sp. ; Vasilevskaya 1972: 53, pls. 17: 4–7; 18: 1–4. 1972 Podozamites pseudolanceolatus ; Vasilevskaya 1972: 54, pl. 19: 3. Etymology: From Latin substrictus, narrow; after the narrow shape of the leaves.

Holotype: NRM S080074 / S080079 (counterparts); axis with alternately arranged leaves; Fig. 9 H.

Type locality: Fleur de Lyshamna, Wedel Jarlsberg Land, Spitsbergen, Svalbard, Norway.

Type horizon: De Geerdalen Formation or Bravaisberget Formation, Kapp Toscana or Sassendalen Group, Upper Triassic (most likely Carnian–Rhaetian).

Diagnosis.— Strap-shaped leaves arranged alternately on prominent axes, slightly tapering towards acutely rounded apex and slender base; venation parallel, veins bifurcating close to the base; leaves amphistomatic, epidermal cells typically isodiametric, stomatal complexes round, guard cells surrounded by 6–7 subsidiary cells each producing one papilla overarching the porus.

Material.— Spitsbergen:Bertilryggen ( NRM S 080255); Midterhukfjellet ( NRM S 080058, S 080059); Fleur de Lyshamna ( NRM S 080074, S 080076, S 080078, S 080079, S 080087, S 080089, S 080104); Wimanfjellet ( VSEGEI 10979-08, 10979-13, 10979-29, 10979-77); Agardhbukta ( VSEGEI 10979-94); Teistberget ( VSEGEI 10979-03, 10979-66, 10979-75). Edgeøya: Kapp Lee ( NRM S 080198, S 080205, S 080217, S 080219, S 080221, S 080222, S 080227– S 080233, S 080237, S 080239); Kvalpynten ( NRM S 080242). Carnian (Upper Triassic).

Description.— Arberophyllum substrictum is characterised by strap-shaped leaves 9–11 mm wide. The longest fragment is 108 mm long suggesting a maximum leaf length of around 120 mm. No petiole is present; the leaf base is poorly preserved but typically <2 mm wide (Fig. 9 L – N). Leaf apices are rounded to acute but not pointed (Fig. 9 I – L). Leaves are more slender than and not as robust as those of A. spetsbergensis ; they taper towards the base and apex more smoothly. Leaves contain distinct but not very prominent parallel veins (Fig. 9 I) with a density of 7–8 veins/cm in mid-lamina. Veins bifurcate one or two times in the basal part of the leaf and proceed to the apex without further bifurcations. Epidermal anatomy is known from one specimen from Wimanfjellet (see Vasilevskaya 1972) and is superficially similar to that of A. florinii from the Carnian of Lunz (cf. Pott et al. 2007d). Two specimens indicate that leaves of A. substrictum were arranged alternately on prominent axes (Figs. 6 A, 9 H).

Remarks.— Arberophyllum substrictum is easily differentiated from A. spetsbergensis by its more slender shape, more gentle apical and basal taper and less densely arranged veins. The arrangement of leaves on the axes is, as far as visible, also different. Podozamites pseudolanceolatus Vasilevskaya, 1972 might belong here, but epidermal anatomy is unknown for that species. Vasilevskaya (1972) published one specimen under the name Glossophyllum sp. , which had a well-preserved cuticle (see Vasilevskaya [1972] for details); this is also assignable to A. substrictum on the basis of its cuticle architecture. Arberophyllum florinii from the Carnian of Lunz is very similar to A. substrictum , but differs in its distinctly smaller size. Podozamites leaves differ from Arberophyllum by the more regular arrangement and architecture of the stomata and the rectangular shape of the epidermal cells ( Doludenko 1967). Unfortunately, no fresh cuticle could be retrieved from any Svalbard specimen even though I tried with one promising sample. Therefore, some of the specimens assigned here to Arberophyllum might in fact be Podozamites , but for an unambiguous assignment, cuticles are essential to reveal the differences in epidermal anatomy (cf. Doludenko 1967).

Geographic and stratigraphic range.— Svalbard; Carnian.