Evolution of Silurian phytogeography, with the first report of Aberlemnia (Rhyniopsida) from the Pridoli of West Junggar, Xinjiang, China

Abstract

The development of phytogeography is an essential aspect of floral evolution. The Silurian is considered a pivotal period for the development of early land vegetation based on both macrofossil and microfossil evidence; however, the evolution of phytogeographic zonation at that time remains controversial. In this paper, we describe a new species of the rhyniopsid, Aberlemnia junggaria sp. nov., from the Pridoli (upper Silurian) of West Junggar, Xinjiang, China. The new plant consists of at least three orders of axes, an oval to reniform terminal sporangium bearing in sparse ultimate axes and sporangium with a nearly enclosed dehiscence line. A dataset of global Silurian macrofossil records was compiled, including 30 species within 24 genera from 38 localities covering 8 main paleogeographic blocks. Using these data, the spatial-temporal distribution of Silurian plant macrofossils was mapped. Biogeographic evolution is revealed for the first time by means of network analysis and cluster analysis, and two phytogeographic realms, the West Junggar-Vietnam and Laurussia-North Gondwana realms are provisionally recognized during the Pridoli Epoch. Considering the widespread microfossil evidence for land plant diversification and dispersal, this global phytogeographic zonation might have onset at an even earlier time.