Study On Cytology And Gametophyte Development Of Cheilanthoid Ferns In China

Due to morphological convergence driven by adaptation to xeric environments,cheilanthoid ferns have been one of the most contentious fern groups in terms of phylogeny and classification.In recent years,the molecular phylogenetic has been widely used in cheilanthoid ferns and related groups with some new results.But these results didn't get the supporting of the cytology and gametophyte development.In this study,we focus on the controversial species of cheilanthoid ferns,such as Pellaea connectens C.Chr.,Notholaena hirsuta(Poir.)Desv.,Cheilosoria tenuifolia(Burm.f.)Trevis.,Sinopteris grevilleoides(Christ)C.Chr.et Ching,Sinopteris albofusca(Bak.)Ching,Aluritopteris niphobola(C.Chr.)Ching and so on.The experiments were carried out by using the traditional cytological method and culturing the spores with mixed media.Combining with the results of molecular systematics,morphology,palynology,and cytology,we discussed the systematic position of these species in the study.The results show that:(1)Pellaea connectens is a sexual tetraploid species with a base chromosome number of x=27,which is consistent with Argyrochosma and different from other cheilanthoid ferns.In addition,the features in the gametophyte development are highly consistent with the members of the genus Argyrochosma.Combining with the previous studies on molecular systematics and morphology,we support the previous taxonomic treatment of removing Pellaea connectens from Pellaea to Argyrochosma.(2)Cheilosoria tenuifolia is a sexual tetraploid species with a base chromosome number of x=27,which is different from Cheilanthes(with x=29 or 30).Notholaena hirsuta has two ploidy levels—apogamous pentaploid and apogamous heptaploid,with a base chromosome number of x=27,which is different from Notholaena(with x=30).The base chromosome number of Cheilosoria tenuifolia is consistent with that of Notholaena hirsuta.Based on the previous results of molecular systematics,morphology and palynology,we think that Cheilosoria tenuifolia and Notholaena hirsuta should be divided into a same genus which is originated in Australia and out of the Asian cheilanthes group.The relationship between the two species and American cheilanthoid ferns,and the relationship between the two species and Australian cheilanthoid ferns are to be studied further.(3)Aluritopteris niphobola is a sexual diploid species with a base chromosome number of x?30.The base chromosome number,the ploidy and reproductive mode of the species are all consistent with those of Sinopteris.In addition,the features in the gametophyte development of Aluritopteris niphobola are highly consistent with the genus Argyrochosma.Combining with the previous evidence of molecular systematics,we think that there is no essential difference between Aluritopteris niphobola.And we support the view that the genus Sinopteris shouid be incorporated into Aluritopteris.(4)Paragymnopteris delavayi is a apogamous triploid species with a base chromosome number of x=c.29.This is the first report on the chromosome number,ploidy and reproductive mode of the species.