Genome size evolution of the extant lycophytes and ferns

Ferns and lycophytes have remarkably large genomes.However,little is known about how their genome size evolved in fern lineages.To explore the origins and evolution of chromosome numbers and genome size in ferns,we used flow cytometry to measure the genomes of 240 species(255 samples)of extant ferns and lycophytes comprising 27 families and 72 genera,of which 228 species(242 samples)represent new reports.We analyzed correlations among genome size,spore size,chromosomal features,phylogeny,and habitat type preference within a phylogenetic framework.We also applied ANOVA and multinomial logistic regression analysis to preference of habitat type and genome size.Using the phylogeny,we conducted ancestral character reconstruction for habitat types and tested whether genome size changes simultaneously with shifts in habitat preference.We found that 2 C values had weak phylogenetic signal,whereas the base number of chromosomes(x)had a strong phylogenetic signal.Furthermore,our analyses revealed a positive correlation between genome size and chromosome traits,indicating that the base number of chromosomes(x),chromosome size,and polyploidization may be primary contributors to genome expansion in ferns and lycophytes.Genome sizes in different habitat types varied significantly and were significantly correlated with habitat types;specifically,multinomial logistic regression indicated that species with larger 2 C values were more likely to be epiphytes.Terrestrial habitat is inferred to be ancestral for both extant ferns and lycophytes,whereas transitions to other habitat types occurred as the major clades emerged.Shifts in habitat types appear be followed by periods of genomic stability.Based on these results,we inferred that habitat type changes and multiple whole-genome duplications have contributed to the formation of large genomes of ferns and their allies during their evolutionary history.

Taxonomic revision of Lepisorus(J.Sm.) Ching sect.Lepisorus(Polypodiaceae) from China

The taxonomy of Lepisorus （J. Sm.） Ching sect. Lepisorus in China was revised based on herbarium specimen examinations, field observations, and microscopic study of rhizome scales, soral paraphyses, leaf epidermis, and spores. As a result, nine species were recognized： Lepisorus macrosphaerus （Baker） Ching, Lepisorus asterolepis （Baker） Ching, Lepisorus marginatus Ching, Lepisorus kuchenensis （Y.C. Wu） Ching, Lepisorus megasorus （C. Chr.） Ching, Lepisorus kawakamii （Hayata） Tagawa, Lepisorus subsessilis Ching ＆ Y.X. Lin, Lepisorus affinis Ching, and Lepisorus nudus （Hook.） Ching. Lepisorus kawakamii （Hayata） Tagawa was reinstated; Lepisorus gyirongensis Ching ＆ S.K. Wu and Lepisorus longus Ching were reduced to synonyms ofL. nudus and L. affinis, respectively. The subdivision ofLepisorus macrosphaerus was not accepted. Rhizome scales and paraphyses are the most useful characters for species delimitation as well as for infrageneric classification. Characteristics of the leaf epidermis and spore ornamentation are usually stable and thus of great significance in understanding the relationships among groups within the genus.

Fossil evidence reveals uplift of the central Tibetan Plateau and differentiated ecosystems during the Late Oligocene

The uplift of different parts of the Tibetan Plateau caused by the collision,subduction and thickening of the Indian-Eurasian continent is considered to be the most significant landform change of Asia in the last 50 Ma.The plateau uplift led to elevation and topographical changes in neighboring areas and created diversified niches for the distribution and migration of plants and animals.The resultant high mountains controlled the South Asian monsoon,preventing the monsoon from crossing the plateau and reaching the hinterland of Asia.