1.5 Statistical analysis
When Gymnosphaera is considered as an independent taxonomic unit at the genus level, the eight species of Cyatheaceae are divided into three genera. That is, Alsophila denticulata, Alsophilapodophylla , Alsophila metteniana , andAlsophila gigantea belong to the genusGymnosphaera ; Alsophila spinulosa andAlsophila costularis belong to the genus Alsophila ; and Sphaeropteris brunoniana and Sphaeropterislepifera belong to the genus Sphaeropteris . WhenGymnosphaera is classified into the genus Alsophila , Cyatheaceae is divided into two genera. The Kruskal-Wallis H test and Mann-Whitney U test in IBM SPSS v22.0 software (Allen et al., 2014) were used to analyze the significance of the differences between taxa when three genera and two genera were assumed, respectively. The statistical results covered the whole chloroplast genome, the SSRs of different unit lengths in the chloroplast genome, and the number, relative abundance, relative density, and GC content of SSRs and SSRs of different unit lengths in the IGS, LSC, intronic, and CDS regions of the chloroplast genome of the eight species of Cyatheaceae. Photovoltaic (PV) cluster analysis using the ward linkage method in R v3.5.1 (R Core Team, 2013) was performed on the SSRs of the chloroplast genome and its IGS regions , LSC regions and on the number, relative abundance, relative density, and GC content of single-nucleotide SSRs of the chloroplast genome with Euclidean distance as the measurement. The number of repetitions is 10,000.