Cytotaxonomic study of Plagiogyria (Plagiogyriaceae) from China

The chromosome numbers and reproductive biology of eight species from fern genus Plagiogyria (Plagiogyriaceae) from China were investigated, finding seven of the eight species (P. adnate, P. assurgens, P. euphlebia, P. glauca, P. japonica, P. pycnophylla, and P. stenoptera) had chromosomal complements of n = 66 (66II), while P. falcata had a chromosomal complement of n = 62 (31II + 31I). The chromosome numbers of three species-P. assurgens, P. falcata, and P. pycnophylla-are here reported for the first time, while other assayed species revealed new cytotypes. Based on observations of homologous chromosome pairing in diakinesis stage meiosis I of spore mother cells, P. falcata is an agamospermous triploid with 64 haploid spores per sporangium. The remaining species are sexual diploids. Three basic chromosome numbers (i.e., x = 62, 65, 66) are found in Plagiogyria. The distribution of species with different basic chromosome numbers indicates the basic chromosome number x = 66 was plesiomorphic, while x = 62 and x = 65 are apomorphic, indicating aneuploidy events have occurred in this genus and showing an evolutionary trend of decreasing chromosome numbers. The distribution of the sexual diploid and tetraploid species and agamospermous triploid species confirmed the origin of this genus to be southwest China, with apparent diffusion into northeast Asia (e.g., Taiwan) and Japan. However, a few species appear to have originated in America.