The Lejeuneaceae are the largest family of the liverworts (Hepaticae), with almost a thousand species in 91 currently accepted genera. We analysed phylogenetic relationships of 69 genera, representing all major subfamilies and tribes recognized in the family, by using 49 informative morphological characters (31 gametophytic, 18 sporophytic), one chemical character, and applying equal and successive weighting of characters and parsimony analysis. In all trees recovered, the Lejeuneaceae were monophyletic with Nipponolejeunea (subfam. Nipponolejeuneoideae) forming the basalmost lineage. The remaining genera clustered in two major groups, the monophyletic Lejeuneoideae (52 genera) and the paraphyletic Ptychanthoideae (16 genera). Within each, several multigeneric lineages corresponding in part to previously described taxa were recovered: the Acrolejeuneinae and Ptychanthinae clades in the Ptychanthoideae, and the Brachiolejeuneinae, Lejeuneeae and Tuyamaella-Cololejeunea clades in the Lejeuneoideae. Bryopteris , a genus sometimes treated as a separate family, was nested in the Ptychanthinae clade. The Tuyamaella-Cololejeunea lineage corresponded with three previously recognized subfamilies (Cololejeuneoideae, Myriocoleoideae and Tuyamaelloideae) and contained genera with neotenic features, in two subclades. These features seemed to have originated by multiple heterochronic events: single origins were detected for 'protonemal neoteny' and 'primary neoteny', whereas 'secondary neoteny' probably evolved twice. Relationships within the large Lejeuneeae clade (43 genera) remained largely unresolved, although several putative lineages were detected in majority rule trees. Additional characters such as DNA sequences may provide better phylogenetic resolution in this group.

Fifteen species of Lejeunea and three species of Taxilejeunea (Lejeuneaceae, subfam. Lejeuneoideae) occurring in Misiones, Argentina are described and illustrated: Lejeunea cancellata Nees & Mont., L. filipes Spruce, L. flava (Sw.) Nees, L. geophila Spruce, L. grossitexta (Steph.) E.Reiner & Goda, L. laetevirens Nees & Mont., L. lepida Lindenb. & Gottsche, L. monimiae (Steph.) Steph., L. phyllobola Nees & Mont., L. ptosimophylla C.Massal., L. puiggariana Steph., L. quinqueumbonata Spruce, L. setiloba Spruce, L. tapajosensis Spruce, L. trinitensis Lindenb., Taxilejeunea obtusangula (Spruce) A.Evans, T. pterigonia (Lehm. & Lindenb.) Schiffn. and T. terricola (Spruce) Steph. Five new synonyms (Lejeunea flava (Sw.) Nees [syn. nov.: L. symphoreta Spruce], L. lepida Lindenb. & Gottsche [syn. nov.: L. cladobola Spruce] and L. phyllobola Nees & Mont. [syn. nov.: L. cephalandra Spruce, L. polycephala Spruce and L. brittoniae (A.Evans) Grolle]) and four lectotypifications (L. lepida Lindenb. & Gottsche, L. monimiae (Steph.) Steph., L. phyllobola Nees & Mont. and L. quinqueumbonata Spruce) are proposed. Keys for identification of the species are also provided.

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