Karyotypes and nuclear DNA amounts in Polypodium L. (Polypodiaceae)

Karyotype studies in several species of Polypodium show that telocentric chromosomes are the most common with acrocentrics forming the remainder of the complement. The relative numbers of these chromosome types can be used as indicators of species relationships although direct comparisons are difficult to make due to the large number of similar-sized chromosomes. The karyotype data support the theory that P. interjectum is a polyploid derived from the hybridization of, P. australe and P. vulgare. Measurements of nuclear DNA content show that the four diploid species P. australe, P. scouleri, P. virginianum and P. glycyrrhiza all have very similar amounts of DNA. The tetraploid P. vulgare has one-and-a-half times the DNA content of the diploids and the hexaploid P. interjectum has two times the DNA content of the diploids. The chromosomes of the tetraploid and hexaploid are smaller than those of the diploids and evolution in Polypodium appears to have been accompanied by either a loss or gain of nuclear DNA; the direction of the change cannot be ascertained by the present study.