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Halimeda is a genus of green seaweed showing high morphological plasticity. Studies using molecular markers for species delimitations and phylogenetics have revealed cryptic diversity and new species throughout the world. Seven species of Halimeda are currently recognized in Brazil. The present study describes the new species Halimeda soniae Ximenes, Oliveira-Carvalho, M. E. Bandeira-Pedrosa et Cassano sp. nov. to accommodate the taxon previously identified as Halimeda aff. gracilis for Brazil. Samples of H. soniae were collected in Espírito Santo State (southeastern Brazil), and plastid gene sequences of tufA and rbcL were obtained. Phylogenetic analyses showed that H. soniae belongs to Section Pseudo-opuntia, together with Halimeda gracilis and Halimeda lacrimosa; the three species have overlapping morpho-anatomical features. Phylogenetic analyses suggest that H. gracilis is restricted to the Indo-Pacific Ocean, whereas the other two species appear to be restricted to the Atlantic. Additional research on Caribbean specimens will be necessary to resolve the taxonomic position of the taxa named as H. lacrimosa and H. gracilis in that region. Based on our results, H. gracilis does not occur in the Brazilian marine flora.

The green algal genus Bryopsis has simple morphology and high phenotypic plasticity, making it difficult to identify its species based on morphological characteristics alone. This study evaluated the diversity of Bryopsis in northeastern Brazil (the State of Pernambuco), based on morphological and molecular data using the markers tufA and rbcL. Molecular analyses were incongruent with morphology, demonstrating the existence of cryptic and polymorphic species in the genus. Of the four taxa cited for the area based only on morphological data (Bryopsis corymbosa, B. pennata, B. plumosa, Bryopsis sp.), only B. pennata was recorded. Typical specimens of B. pennata and B. plumosa were grouped with low genetic divergence, 0-0.21 % for tufA and no divergence for rbcL, indicating that B. pennata is an extremely plastic species that includes specimens with morphotype B. "plumosa". Bryopsis pennata var. secunda is cited for the first time for northeastern Brazil, with divergence from the typical variety of 0.96-1.57 % for tufA and 0.4 % for rbcL. This study showed that broader sampling of Bryopsis is necessary in order to confirm the taxonomic status of the species referenced for Brazil, whose phenotypic plasticity may cause overestimation of diversity or reveal cryptic species.

A B S T R A C TThis study evaluated the influence of the shoot density of the shoal grass Halodule wrightii on the composition of the associated algal community, in rocky and sandy habitats on the coast of Ceará in northeastern Brazil. The phycological community included 18 species in 10 families, members of Rodophyta (72.2%), Chlorophyta (22.2%) and Phaeophyceae (5.5%). The largest proportion were epilithic (50%), followed by epiphytes on H. wrightii (38.4%), epipsammics (8%), and epiphytes on other algae (4%). Epiphytes on H. wrightii occurred mainly associated with rhizomes, but also tendrils of H. musciformis occurred attached to the leaves. The phycological community varied according to the density of H. wrightii, independently of particular characters of the meadows, although both habitat and other environmental variables seemed to influence the macroalgae composition and diversity. The rocky habitat was more diverse than the sandy habitat, but in the sandy habitat the shoal grass was important for algal settlement in areas where hard substrates were scarce or absent. R E S U M OEste estudo avaliou a influência da densidade do capim-agulha Halodule wrightii sobre a composição da comunidade algal associada, em habitats rochosos e arenosos da costa do Ceará, Nordeste do Brasil. A comunidade ficológica incluiu 18 espécies em de 10 famílias, integrantes de Rodophyta (72.2%), Chlorophyta (22.2%) e Phaeophyceae (5.5%). A maior proporção foi epilítica (50%), seguida pelas epífitas de H. wrightii (38.4%), epífitas de outras algas (8%) e epipsâmicas (4%). Epífitas de H. wrightii ocorreram associadas com os rizomas, mas gavinhas de H. musciformis ocorreram presas às folhas. A comunidade ficológica variou de acordo com a densidade de H. wrightii independentemente das características particulares dos prados estudados, embora tanto o habitat quanto outras variáveis ambientais pareceram influenciar a composição e diversidade das macroalgas. O habitat rochoso foi mais diverso que o arenoso, mas no habitat arenoso o capimagulha foi importante para o assentamento de algas em áreas onde substratos duros foram raros ou ausentes.

Udotea is an exclusively marine green macroalgal genus with wide distribution in both tropical and subtropical regions. Due to the difficulty in properly delimiting infrageneric taxa based on morpho-anatomical characteristics by the presence of cryptic species and phenotypic plasticity, the use of techniques of DNA barcode and phylogenetic analysis have been fundamental to assess the Udotea species diversity. Information concerning this genus in Brazil is currently restricted to a few publications in checklists and/or regional floristic surveys along the tropical coast. This study aimed to evaluate the diversity of Udotea in northeastern Brazil through morphological-based taxonomy allied with plastid molecular markers, tufA and rbcL. We generated phylogenies of Udotea sensu lato, and we used different species delimitation methods to assess the diversity among sequences of selected tufA clades within Udotea sensu stricto. None of the eight infrageneric taxa reported for Brazil based only on morphology were confirmed by using molecular data. Udotea dotyi was revealed by tufA and rbcL sequences and represents its first occurrence for the western south Atlantic Ocean. A taxon named here as ‘Udotea cyathiformis’ requires further studies for its definition. This first molecular study on Udotea from the Brazilian coast shows that a broader sampling will be necessary to assess the true diversity of the genus in the western south Atlantic, which may be overestimated due to its high morphological plasticity.