Fertile organs and in situ spores of Marattia asiatica (Kawasaki) Harris (Marattiales) from the Lower Jurassic Hsiangchi Formation in Hubei, China

Abstract

The fertile organs and in situ spores of Marattia asiatica (Kawasaki) Harris from the Lower Jurassic Hsiangchi Formation in Zigui, Hubei Province, China, are studied using light microscopy and scanning electron microscopy. The emended diagnosis is given based on studies on the variation of gross morphology and the internal structures of synangia and in situ spores. Morphologically, this Asiatic species is distinguished from other European ones mainly in the more crowded veins and longer synangia. The linear synangia of M. asiatica are bivalved and attached on the secondary veins at the pinna margin. A synangium is composed of two long strips of laterally joined and triangular sporangia. Each sporangium contains a large number of monolete spores with granular exine and a small size (average 25 μm), resembling the dispersed genus Marattisporites. Geographically, M. asiatica is recorded between 22 and 42°N in East Asia and Middle East. The species is distributed in the Upper Triassic–Lower Jurassic of China in both the southern and northern phytoprovinces. Extant Marattia seems to have evolved via reduction of pinna form, venation and especially synangia from some of the Mesozoic and Paleozoic members.