Thyrsopterorachis, gen. nov., a tree fern rachis from the upper cretaceous of Hokkaido, Japan

Abstract

Thyrsopterorachis mesozoica, gen. et sp. nov from the upper Cretaceous of Hokkaido, Japan, is described with diagnosis. It closely resembles the extant genusThyrsopteris in its general vascular patterns and histological features.Thyrsopterorachis, however, exhibits a three-parted adaxial vascular system that is arranged in a C-shape instead of the continuous pattern found inThyrsopteris. This is the first report of the fern family Thyrsopteridaceae in the Northern Hemisphere.