Abstract
Many traditional genera of the Halymeniaceae turn out to be poly- or paraphyletic based on molecular phylogenies. The genus Halymenia is no exception. In this study, we provide a detailed characterization of the vegetative and reproductive morphology of the generitype of Halymenia, H. floresii, based on specimens from the north-western Mediterranean Sea. In addition we describe a newly detected clade (Neofolia rosea gen. et sp. nov.) which was previously confused with ‘Halymenia latifolia’ from the north-eastern Atlantic Ocean and the western Mediterranean Sea. The development of auxiliary cell ampullae in Neofolia and Halymenia is similar, namely, ampullae consist of three orders of branched filaments after diploidization of the auxiliary cell and form a weak pericarp comprised only of elongated and branched ampullary filaments. The auxiliary cell is always differentiated from the first cell of the third-order ampullary filament. This pattern differs significantly from previous descriptions of the female reproductive system of Halymenia, in which the auxiliary cell is said to be the third cell of the primary ampullary filament and few secondary and tertiary ampullary filaments are produced from the primary ampullary filament before diploidization of the auxiliary cell. Neofolia primarily differs from Halymenia in the absence of a cellular cluster (= nutritive filaments), which is present in the basal parts of the carpogonial branch ampullae in Halymenia. Moreover, auxiliary cell ampullary filaments in Neofolia are much shorter (6–7 cells long) than those found in Halymenia (9–13 cells long), and the secondarily generated connecting filaments are issued from the basal cells of the ampullary filaments in Halymenia, whereas they are produced from the fusion cell in Neofolia. Resolving the polyphyly of Halymenia will require a re-examination of the species of ‘Halymenia’ that are not clustered with the generitype
