Hymenasplenium Hayata, Bot. Mag.

Kessler, Michael & Smith, Alan R., 2018, Prodromus of a fern flora for Bolivia. XXIX. Aspleniaceae, Phytotaxa 344 (3), pp. 259-280 : 259-280

Hymenasplenium Hayata, Bot. Mag. (Tokyo) 41: 712. 1927.

This is the sister genus to Asplenium , recognized mainly by the creeping and dorsiventral rhizomes with the leaves arranged in two lateral rows, and the swollen petiole bases ( Regalado & Prada 2011, Ohlsen et al. 2015). In contrast, Asplenium has erect to creeping rhizomes with the leaves weakly to decidedly radially arranged, and lacks swollen petiole bases. In addition, Hymenasplenium has a chromosome base number of x = 38 or 39, whereas Asplenium has x = 36 (rarely 35) ( Mitui et al. 1989). Species with occasional back-to-back sori (e.g., H. delitescens ) can be confused with Diplazium ( Smith 1976) , but that genus generally lacks clathrate rhizome scales. In addition, the two genera are separated by obscure characteristics such as the number of annular cells, number of sporangial stalk cells, and the form of petiolar vascular bundles ( Mitui et al. 1989). Hymenasplenium is pantropical and has about 25 species, with 11 species in the Neotropics ( Smith 1976, Murakami & Moran 1993, Murakami & Schaal 1994, Moran & Sundue 2004, Regalado & Prada 2011).