The section Thamnopteris is morphologically distinct among the large fern genus Asplenium, but the species recognition within this section is very difficult. To understand the species concept of this section from a cytological view, I examined chromosome numbers of fifteen samples representing eight taxa (species and intraspecific taxa). As result, seven taxa were determined to be sexual tetraploids with chromosome number 2n  =  144 and Asplenium humbertii is a sexual hexaploid with 2n  =  216. Along with the chromosome numbers reported, notes on nomenclature, diagnostic characters, and geographical distribution for the eight taxa are given. Cytological data available so far indicate that Asplenium sect. Thamnopteris is not a monophyletic group.