A taxonomic review of the Amazonian rheophyte Schusterolejeunea Grolle (Lejeuneaceae: Cololejeuneinae), with two new combinations

Schusterolejeunea inundata (Spruce) Grolle is a widespread, yet poorly known species restricted to riparian habitats of the Amazon Basin in northern South America. Since its original description by Richard Spruce in 1884, phenotypic differences among populations convinced the original author to split the taxon into two varieties. An extensive review of Schusterolejeunea Grolle specimens hailing from disparate regions of the Amazon Basin has provided convincing evidence of discontinuities among leaf, lobule, and perianth morphology offering support for a novel taxonomic proposal. In the present review, the genus Schusterolejeunea encompasses two species, S. inundata and the newly elevated species Schusterolejeunea saxorum (Spruce) A.M.Sierra & C.E.Zartman, stat. nov., comb. nov., which differs from S. inundata by its oblong leaves, with large rectangular to oblong lobules, that cover 1/3-2/3 of the leaf lobe, and the perianth with five indistinct low keels. The variety Schusterolejeunea inundata var. fontinaloides (Spruce) A.M.Sierra & C.E.Zartman, comb. nov. is considered a distinct taxon, distinguished from S. inundata var. inundata by its ovate leaves, and lobules on the primary stem triangular with a longer keel extending 6-12 cells long. For each taxon, we present a detailed morphological description, current geographical distribution, and illustrations.