A dipteridaceous fern with in situ spores from the Lower Jurassic in Hubei, China

Abstract

Dictyophyllum, a genus of the fern family Dipteridaceae, was widespread during the Triassic and Jurassic. However, the in situ spores are relatively poorly known. The specimens described here represent the first report of fertile fronds with in situ spores from Asia. Well-preserved and compressed specimens of the dipteridaceous fern Dictyophyllum nilssonii (Brongniart) Goeppert were investigated from the type locality of the Hsiangchi Flora in western Hubei province, southern China, collected from the upper part of the Lower Jurassic Hsiangchi Formation. Sporangia and in situ spores were examined using light and electron microscopes. The sporangia are rounded, 300–450 µm in diameter, with an oblique annulus. Each sporangium produces 220–280 trilete spores. These are triangular to subtriangular in outline, 40 µm in average diameter, with smooth exines, as well as interradial thickenings along the laesura situated on the proximal surface. The in situ spores are comparable to the dispersed trilete spore genus Dictyophyllidites. Preliminary observations on the ultrastructure of the in situ spores are reported, which supply clues for further investigation of the systematics and phylogeny of the Dipteridaceae. In addition, the ecological implications of Dictyophyllum and its associated ferns are briefly discussed.