Adenophorus s.l. is one of only three endemic genera of ferns in Hawaii. It has been distinguished from other genera of Grammitidaceae primarily because of distinctive glandular paraphyses and other laminar hairs. The uniqueness of those features, however, has been questioned and other Indo-Pacific taxa may be close relatives. In particular, Chrysogrammitis musgraviana was proposed as being the closest Indo-Pacific relative. Hawaiian species have either been classified as a single genus with two subgenera or as two similarly circumscribed genera: Adenophorus s.s., with variously deeply dissected leaves and no root buds, and Oligadenus, with entire or shallowly-to-deeply lobed leaves and with root buds. We investigated the phylogenetic relationships of the species of Adenophorus s.l. with one another and with 56 other species of the Grammitidaceae from throughout the range of the family, including other Hawaiian taxa. We obtained DNA sequences of three cpDNA regions: atpB, rbcL, and the trnL-trnF spacer. Phylogenetic analyses of these data yield the following hypotheses: 1) Adenophorus s.l. is monophyletic; 2) the Hawaiian endemic Grammitis tenella is the sister taxon to Adenophorus s.l.; 3) Adenophorus s.s. is monophyletic and arose from within subgenus Oligadenus; 4) subgenus Oligadenus is paraphyletic; and, 5) C. musgraviana is not closely related to the Hawaiian clade. The geographical origin of the group remains unresolved because the strongly supported sister clade contains species from Costa Rica, Panama, Brazil, and La Réunion.

Key words: Adenophorus, ferns, Grammitidaceae, Hawaii, phylogenetics, systematics