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The exploration of seaweed diversity in poorly studied habitats has often led to the discovery of new species. Sandcovered rocks are an example, as they received less attention than sand-free rocky intertidal habitats during seaweed diversity surveys in Brazil. In sand-covered rocks from Espírito Santo and Rio de Janeiro we found an alga whose morphology was unique among rhodomelacean species previously reported in Brazil. With the aim to clarify the taxonomic identity of this species we studied its morphology, as well as its phylogenetic relationships. Molecular analyses resolved this species in the genus Alsidium (tribe Alsidieae) and differed from sequenced congeners with divergences ≥2.5 and 4.2% in the rbcL and cox1 genes, respectively. Morphological characters were in agreement with the genus Alsidium, and differed from other species currently recognized in the genus. The species consisted of a basal crust and scarcely branched erect axes with seven pericentral cells covered by a continuous layer of cortical cells. Reproductive structures were formed on clusters of short determinate branches. Therefore, the new species A. oliveiranum is proposed based on morphological and molecular evidence. Our findings contribute to better understand the diversity of the tribe Alsidieae, which is particularly diverse in the Americas. [ABSTRACT FROM AUTHOR]

The vegetative and reproductive morphology of the crustose red alga Peyssonnelia japonica (Segawa) Yoneshigue was re-examined based on the holotype specimen and recent collections from various localities in Japan, including the type locality, and Hawaii. This species is characterized by the following features: thallus with appressed margins, perithallial filaments arising from the entire upper surface of each hypothallial cell (the Peyssonnelia rubra-type), easily separable perithallial filaments in a gelatinous matrix, hypothallial filaments arranged in parallel rows, unicellular rhizoids, hypobasal calcification, gonimoblasts derived mainly from connecting filaments, and spermatangia produced in a series of whorls comprised of one to four paired spermatangia surrounding each central cell (the Peyssonnelia dubyi-type). In addition to these features, the dimensions of the vegetative and reproductive structures of Peyssonnelia boudouresquei Yoneshigue described from Brazil were consistent with those of P. japonica. Molecular phylogenetic analyses using partial 26S rDNA, rbcL, and cox2-3 spacer DNA sequences also supported the monophyly of P. japonica (from 16 localities in Japan and one locality in Hawaii) and P. boudouresquei (from two localities in Brazil). Therefore, P. boudouresquei may be a taxonomic synonym of P. japonica. However, considering the relatively high sequence divergences between the two taxa (2.1–2.5% in partial 26S rDNA, 5.9–6.7% in rbcL, and 5.8–6.7% in cox2-3 spacer), and the relatively limited geographic sampling ranges, we reserve the taxonomic conclusion until further morphological and genetic data of the specimens from other geographic areas connecting Japan and Brazil become available. [ABSTRACT FROM AUTHOR]