Leaf scar and petiole anatomy reveal Pecopteris lativenosa Halle is a marattialean fern

Pecopteris (Brongniart) Sternberg is a morphological fossil genus with a cosmopolitan distribution during the Permo–Carboniferous, of which most species belong to the marattialean and or “filicalean” ferns or less frequently to pteridosperms. The taxonomic affinity is uncertain unless distinctive reproductive organs or rachis anatomy is known. Among the numerous species of Pecopteris in the Permian Wuda Tuff Flora, Inner Mongolia, China, Pecopteris lativenosa Halle has been considered as a pteridosperm based on its larger variation of frond morphology, although evidence of fertile organs or rachises are unknown. Newly discovered specimens of this species from the Wuda Tuff Flora are mostly impression fossils. However, some have partially permineralized petioles and have fronds in organic connection to Caulopteris-type stem. Fronds are tripinnate; penultimate pinnae lengths are variable as are ultimate pinnae lengths. Pinnules are oval and thick, and their midveins are straight and are of stable thickness. Lateral veins are dense, bifurcating 1–3 times. Petiole and rachises are anatomically preserved and show sclerenchyma, fundamental tissue and vascular tissue. Vascular bundles of petioles and rachises are C-shaped with two laterally inrolled ends, which are typically stewartiopterid petiole/rachis of Marattiales. These features allow us to assign Pecopteris lativenosa to the late Paleozoic marattialean family Psaroniaceae.