Rhytimenia, a new genus of red algae based on the rare Kallymenia maculata (Kallymeniaceae, Rhodophyta)

Morphological and molecular analyses of newly collected samples of the rare Kallymenia maculata, described originally from specimens collected during the Siboga Expedition but never recollected, indicated that the species was incorrectly placed in the genus Kallymenia and did not conform to any existing genera. The new genus Rhytimenia is described to accommodate this species, distinguished morphologically by its gelatinous, bullate thallus; angular (in surface view) outer cortical cells; wholly filamentous medulla lacking ganglionic or refractive cells; and monocarpogonial branch system with spherical subsidiary cells. The autonomy of Rhytimenia was supported by molecular analyses (COI-5P, nuclear ribosomal large subunit gene, rbcL) that resolved K. maculata as only distantly allied to other Kallymeniaceae and clearly incorrectly assigned to Kallymenia based on the position of the generitype Kallymenia reniformis. A second species, Rhytimenia cerebriformis (basionym Sebdenia cerebriformis), was included in the new genus based on molecular analyses and morphological similarities with Rhytimenia maculata but differing in the presence of multiple marginal cartilaginous holdfasts.