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Specimens attributed to the genus Lithophyllum were collected during multiple surveys conducted along the Brazilian coast. These specimens were studied using DNA sequences from three molecular markers (COI5P, psbA, rbcL) and comparative morphoanatomical analyses. This approach revealed eight distinct, well-supported lineages: two currently known species, Lithophyllum atlanticum and L. kaiseri; four new species, L. brasiliense sp. nov., L. pseudomargaritae sp. nov., L. solis sp. nov. and L. tomitae sp. nov.; and two additional lineages that remain unresolved as the available data were incongruent or insufficient. Lithophyllum pseudomargaritae was morpho-anatomically similar but distantly related to sequences from the type locality of specimens morphologically identified as L. margaritae. This study confirms the occurrence of cryptic/pseudocryptic coralline diversity in the Brazilian flora. [ABSTRACT FROM AUTHOR]

Molecular data related to morphology from the multicellular vesiculated genus Dictyosphaeria are scarce. We provide the first molecular data on Dictyosphaeria species from the southwestern Atlantic Ocean, sampled from the Brazilian northeastern coast, and two oceanic islands (Trindade, southeastern Brazil, and Fernando de Noronha, northeastern Brazil). The samples from Brazil were morphologically identified as Dictyosphaeria versluysii and D. ocellata. Our newly generated sequences of D. versluysii formed a monophyletic clade, while their relationship with D. versluysii from the Indo-Pacific Ocean, where the type locality of the species is located, was unresolved. Additionally, the newly generated sequences of D. ocellata confirm its status as a distinct species but reinforce the difficulties in morphologically separating this species. These results might be indicative of cryptic diversity in D. versluysii and highlight the need for molecular data from other geographic locations to understand the diversity and distribution of Dictyosphaeria species. [ABSTRACT FROM AUTHOR]

DNA sequence analyses have demonstrated that Gelidium as currently circumscribed is not monophyletic and has three distinctive lineages: Gelidium sensu stricto that includes the generitype Gelidium corneum, the Capreolia group, and another lineage that includes two distinct clades formed by species from the eastern Pacific and western Atlantic Oceans. A new genus of small gelidioid algae, Gelidiorariphycus, is described to accommodate one of the clades in this latter lineage. Four species (Gelidiorariphycus loratus, G. gahunbooi, G. stipitatus and G. sungminbooi) segregated into this genus in single- and multi-gene phylogenies. Gelidiorariphycus is sister to a clade formed by an unidentified eastern Pacific species and Gelidium lingulatum. These clades are closely related to a clade formed by Gelidiophycus and the Capreolia group. All four Gelidiorariphycus species were morphologically similar with small thalli that have simple and distally flattened erect axes. Fertile tetrasporophytes were found to have sori with sterile margins that are acutely tapered, which may be morphologically distinctive, but determining this requires additional study. These species were rare, with only one or two samples of each collected despite Gelidiales surveys having been done in the areas where they are known. They were mainly found growing on shallow subtidal rocky shores, but a G. gahunbooi specimen was also collected at more than 30 m depth. Their small size and preference for subtidal habitats may explain the small number of specimens collected. The recognition of this new genus is a further step in the establishment of a natural classification system for genera within the Gelidiaceae. [ABSTRACT FROM AUTHOR]

Molecular studies have revealed cryptic diversity and polyphyly in the genus Lithothamnion. In this study we aimed to investigate the diversity and phylogeny of specimens that are morphologically described as Lithothamnion based on extensive collections along the Brazilian coast and an integrative taxonomic approach. Our results led to the proposal of Roseolithon gen. nov. belonging to the subfamily Melobesioideae. This new genus is described from the tropical north-western Atlantic and warm temperate south-western Atlantic specimens, based on phylogenetic analyses of psbA, rbcL-3P, COI-5P and SSU rDNA molecular markers, species delimitation methods, genetic divergence and morpho-anatomical observations. The integrative approach led us to find a set of morphological features that characterize Roseolithon: (i) thallus organization monomerous with plumose hypothallus (non-coaxial); (ii) flared epithallial cells; (iii) subepithallial cells varying in size and may be shorter, approximately equal to or longer than those subtending them; (iv) cells of adjacent filaments linked by fusions; (v) tetra/bisporangial conceptacle chambers multiporate; and (vi) the presence of pore canals bordered by rosette cells in depressions giving the surface a pitted appearance. Depending on the species, this pitted appearance occurs due to the sunken or disintegrated rosette cell roofs. The grade of the degeneration of the rosette cell roofs characterizes the species of this genus. The new genus Roseolithon is composed of at least 18 species, of which we describe seven new species: Roseolithon tupii, R. tamoioi, R. tremembei, R. potiguarae, R. karaiborum, R. purii and R. goytacae. Highlights Phylogenetic analyses revealed Lithothamnion to be a polyFphyletic genus. Integrative taxonomy enabled the description of a new genus Roseolithon. Morpho-anatomy does not reflect molecular phylogeny of non-geniculate coralline algae. [ABSTRACT FROM AUTHOR]

Latitudinal diversity gradients have provided many insights into species differentiation and community processes. In the well‐studied intertidal zone, however, little is known about latitudinal diversity in microbiomes associated with habitat‐forming hosts. We investigated microbiomes of Fucus vesiculosus because of deep understanding of this model system and its latitudinally large, cross‐Atlantic range. Given multiple effects of photoperiod, we predicted that cross‐Atlantic microbiomes of the Fucus microbiome would be similar at similar latitudes and correlate with environmental factors. We found that community structure and individual amplicon sequencing variants (ASVs) showed distinctive latitudinal distributions, but alpha diversity did not. Latitudinal differentiation was mostly driven by ASVs that were more abundant in cold temperate to subarctic (e.g., Granulosicoccus_t3260, Burkholderia/Caballeronia/Paraburkholderia_t8371) or warm temperate (Pleurocapsa_t10392) latitudes. Their latitudinal distributions correlated with different humidity, tidal heights, and air/sea temperatures, but rarely with irradiance or photoperiod. Many ASVs in potentially symbiotic genera displayed novel phylogenetic biodiversity with differential distributions among tissues and regions, including closely related ASVs with differing north‐south distributions that correlated with Fucus phylogeography. An apparent southern range contraction of F. vesiculosus in the NW Atlantic on the North Carolina coast mimics that recently observed in the NE Atlantic. We suggest cross‐Atlantic microbial structure of F. vesiculosus is related to a combination of past (glacial‐cycle) and contemporary environmental drivers. [ABSTRACT FROM AUTHOR]

A unique algal bed formation, composed largely of free-living geniculate coralline algae (articuliths), was recorded within the subtidal zone of Arraial do Cabo Bay, Brazil. The importance of these articuliths was shown by previous ecological surveys, which, using morpho-anatomical analyses, identified these algal specimens as belonging to Amphiroa beauvoisii, Jania adhaerens and J. capillacea. Cryptic diversity was recently found in Brazilian corallines and prompted the reassessment of the species diversity of the Arraial do Cabo Bay algal bed. Here we identified the species of geniculate coralline algae commonly associated with the subtidal beds of Arraial do Cabo Bay using a combination of molecular (psbA) and morpho-anatomical analyses, and compared them to closely related species described for Brazil and elsewhere. Two species belonging to the genera Amphiroa and Jania were identified as the major components of these algal beds. Our analyses suggest that these specimens belong to Amphiroa cf. exilis and to a new species of Jania, Jania cabista sp. nov. [ABSTRACT FROM AUTHOR]

Hypnea is a monophyletic genus with a complex nomenclatural and taxonomic history, and is an important commercial source of carrageenan. Phylogenies of this genus have been accessed based primarily on Asian species; however, recent studies performed in South America revealed a great diversity of species, for which phylogenetic relationships need to be evaluated. Three infrageneric sections are recognized in the genus: Pulvinatae, Spinuligerae, and Virgatae; however, morphological and molecular circumscriptions within each section lack clarity. In this study, we analyzed three distinct markers to establish phylogenetic relationships among Hypnea species. To assign each species to the correct section, morphological data were obtained from original descriptions, reference literature, and comparisons with type/topotype and herbaria specimens. Our analyses recovered robust phylogenies for the genus and provided new insights on the taxonomic status and relationships among and within Hypnea species. The combination of three genetic markers increased the resolution and support, resulting in the largest and best-resolved phylogeny of the genus to date. Single and combined analyses revealed that the three sections of the genus Hypnea are taxonomically irrelevant, as currently recognized. Morphological differences are not associated with monophyletic groups and similarities among clades could be better explained by convergent evolution in thallus habit. [ABSTRACT FROM AUTHOR]

Populations of the marine benthic red macroalgae Hypnea musciformis and Hypnea pseudomusciformis along the Atlantic and Pacific Oceans were tested for phylogeographic structure using the DNA barcode COI-5P combined with rbcL for the construction of the phylogenetic tree. Strong patterns of genetic structure were detected across 210 COI-5P DNA sequences, and 37 COI-5P haplotypes were found, using multiple statistical approaches. Hypnea musciformis was found in the Northeast and Northwest Atlantic, the Mediterrean Sea, Namibia, and along the Pacific coast of Mexico. Two new putative species were detected, Hypnea sp. 1 in the Caribbean Sea and Hypnea sp. 2 in the Dominican Republic. Three distinct marine phylogeographic provinces were recognized in the Southern Hemisphere for H. pseudomusciformis: Uruguay, South-Southeast Brazil, and Northeast Brazil. The degree of genetic isolation and distinctness among these provinces varied considerably. The Uruguay province was the most genetically distinct, as characterized by four unique haplotypes not shared with any of the Brazilian populations. Statistically significant results support both, isolation by distance and isolation by environment hypotheses, explaining the formation and mantainance of phylogeographic structuring along the Uruguay-Brazil coast. Geographic, taxonomic and molecular marker concordances were found between our H. pseudomusciformis results and published studies. Furthermore, our data indicate that the Hawaiian introduced populations of H. musciformis contain Hypnea sp. 1 haplotypes, the current known distribution of which is restricted to the Caribbean. [ABSTRACT FROM AUTHOR]

This study represents the efforts of a network of researchers to characterise the large, floating Sargassum (Fucales, Phaeophyceae) biomass that had reached the Brazilian coast in 2014 and 2015. Material collected during these events was identified as Sargassum natans and S. fluitans using morphological characteristics; ITS2 sequences showed low divergence (0%-3%) with sequences of nine other Sargassum species. Several epiphytic macroalgae, invertebrates and fishes were associated with the floating Sargassum. Satellite images did not support the hypothesis of slicks moving south from the Sargasso Sea in the northern Atlantic Ocean. This strengthens the hypothesis that there is a matrix of pelagic Sargassum in the central Atlantic Ocean and that biomass accumulation should be considered a result of the combination of physicochemical seawater conditions and biological interactions. The biomass accumulation of the stranded Sargassum was estimated during four events, peaking in 98 kg m−2 wet weight on a beach on the Amazonian coast. The landing of huge Sargassum biomass represents a potential source of environmental stress, as it can lead to an increase in oxygen demand and eventually synthesise and release chemical compounds with allelopathic properties. On the other hand, these floating islands are a fundamental element of the biogeography and macroecology of tropical environments in the Atlantic Ocean, providing connectivity south/north and east/west among marine biodiversity from Atlantic reef environments. Studies concerning Sargassum effects on local communities are necessary for the proper management of this phenomenon. [ABSTRACT FROM AUTHOR]

Hypnea has an intricate nomenclatural history due to a wide pantropical distribution and considerable morphological variation. Recent molecular studies have provided further clarification on the systematics of the genus; however, species of uncertain affinities remain due to flawed taxonomic identification. Detailed analyses coupled with literature review indicated a strong relationship among H. aspera, H. cervicornis, H. flexicaulis, and H. tenuis, suggesting a need for further taxonomic studies. Here, we analyzed sequences from two molecular markers ( COI-5P and rbcL) and performed several DNA-based delimitation methods ( mBGD, ABGD, SPN, PTP and GMYC). These molecular approaches were contrasted with morphological and phylogenetic evidence from type specimens and/or topotype collections of related species under a conservative approach. Our results demonstrate that H. aspera and H. flexicaulis represent heterotypic synonyms of H. cervicornis and indicate the existence of a misidentified Hypnea species, widely distributed on the Brazilian coast, described here as a new species: H. brasiliensis. Finally, inconsistencies observed among our results based on six different species delimitation methods evidence the need for adequate sampling and marker choice for different methods. [ABSTRACT FROM AUTHOR]

The diversity of branched Halymenia species in Brazil was assessed by molecular analyses and morphological examination to clarify the status of taxa previously identified as Halymenia floresii and H. pseudofloresii. Molecular tools included sequencing the COI-5P molecular marker for DNA barcoding and rbcL for phylogenetic inferences. Both molecular and morphological results demonstrated that Brazilian specimens previously attributed to H. floresii and H. pseudofloresii do not correspond to these species but constitute three distinct lineages that we propose as the new species: Halymenia ignifera sp. nov., Halymenia pinnatifida sp. nov. and Halymenia silviae sp. nov. We propose that H. floresii and H. pseudofloresii be removed from the Brazilian marine flora. We highlight that without the use of molecular tools, the morphological divergences observed in Brazilian specimens could be misinterpreted as morphological plasticity and lead to incorrect species determinations. [ABSTRACT FROM AUTHOR]

Grateloupia turuturu is a Pacific native species with invasive behaviour that leads to a wide distribution around the world. This study reports collections of fertile tetrasporophytes and female gametophytes of G. turuturu on southern Brazilian coasts and constitutes its first record for the south-western Atlantic. The identity of G. turuturu was confirmed through molecular (COI-5P and rbcL markers) and morphological assessments. Putative paths of introduction are discussed. [ABSTRACT FROM AUTHOR]

Morphological identification of species in the order Gelidiales can be difficult and controversial because of phenotypic plasticity, the low numbers of reproductive specimens and poorly defined taxonomic boundaries. A DNA barcoding survey of Brazilian specimens of Gelidiales, employing neighbor-joining and Automatic Barcode Gap Discovery analyses, indicated the presence of 23 statistically robust primary species hypotheses (PSH). In addition to the cytochrome oxidase I gene (COI-5P), the chloroplast universal plastid amplicon (UPA) marker was also sequenced and submitted to the same analyses. Representatives of each COI-5P/UPA PSH were selected for rbcL sequence analysis to further corroborate the occurrence of 23 species and to infer their phylogenetic relationships. These analyses confirmed the identity of six species previously cited for Brazil: Gelidiella acerosa, G. ligulata, Gelidium crinale, G. floridanum, Pterocladiella bartlettii and P. capillacea. Three new reports for Brazil were also detected: Gelidium microdonticum, Pterocladiella beachiae and P. australafricanensis. Fourteen species remain unidentified and require detailed morphological evaluation. [ABSTRACT FROM AUTHOR]

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Photoprotection of the agarophyte red alga Gracilaria tenuistipitata against ultraviolet radiation (UVR) was investigated in algae submitted for 1 week to photosynthetically active radiation (PAR, 260 μmol photons m-2 s-1) or PAR + UVR (UV-A, 8.13 W m-2 and UV-B, 0.42 W m-2) under different nitrogen concentrations: 0, 0.1, and 0.5 mM of NO3-. Photosynthetic pigments decreased during the time of the experiment mainly under low nitrogen supply and UVR. Incubation under high nitrogen supply (0.5 mM) sustained the photosynthetic levels over time. In contrast, mycosporine-like amino acids (MAAs) increased up to eightfold in the presence of UVR and 0.5 mM NO3-. Under PAR + UVR, maximal quantum yield was positively correlated to MAA abundance, whereas under PAR no correlation was found. The photosynthetic yield of algae cultivated during seven days under PAR + UVR was less affected by a 30-mm exposure of high UVR (16W m-2) and fully recovered after transferring to low PAR irradiances, whereas algae kept under PAR were more affected by UV exposure and no full recovery was observed. Growth rates decreased after three days in the presence of UVR and under low nitrate supply. However, these rates were similar when compared with treatments of PAR and PAR + UVR after seven days, with the exception of samples in 0 mM NO3-, indicating that the acclimation after one week's exposure is related to nitrate supply. In conclusion, the lowest negative effect of UVR on photosynthesis and growth rate in high N-supply-grown algae could be explained by the stimulation of photoprotection mechanisms, such as accumulation of MAAs. Photostimulation of MAA accumulation by UVR under high N supply was observed in G. tenuistipitata even after 20 years in culture without the induction of this photomorphogenic light signal. [ABSTRACT FROM AUTHOR]

This study evaluated the phylogenetic relationship among samples of 'Chantransia' stage of the Batrachospermales and Thoreales from several regions of the world based on sequences of two genes-the plastid-encoded RUBISCO LSU gene ( rbcL) and the nuclear SSU ribosomal DNA gene (SSU rDNA). All sequences of ' Chantransia macrospora' were shown to belong to Batrachospermum macrosporum based on both molecular markers, confirming evidence from previous studies. In contrast, nine species are now associated with ' Chantransia pygmaea,' including seven species of the Batrachospermales and two of the Thoreales. Therefore, the presence of ' C. macrospora' in a stream can be considered reliable evidence that it belongs to B. macrosporum, whereas the occurrence of ' C. pygmaea' does not allow the recognition of any particular species, since it is associated with at least nine species. Affinities of 'Chantransia' stages to particular taxa were congruent for 70.5% of the samples comparing the rbcL and SSU analyses, which were associated with the same or closely related species for both markers. Sequence divergences have been reported in the 'Chantransia' stage in comparison to the respective gametophyte, and this matter deserves further attention. [ABSTRACT FROM AUTHOR]

Laurencia marilzae is recorded for the first time from the western Atlantic Ocean; it was found in Laje de Santos Marine State Park, São Paulo, southeastern Brazil. The specimens were collected in the rocky subtidal zone from 7 to 15 m depth. The most distinctive characteristic of this species is the presence of corps en cerise in all cells of the thallus, including cortex, medulla, and trichoblasts. The phylogenetic position of the species was inferred by analysis of the chloroplast-encoded rbcL gene sequences from 43 taxa, using two other rhodomelacean taxa and two members of the Ceramiaceae as outgroups. Within the Laurencia assemblage, L. marilzae from Brazil and from the Canary Islands (type locality) formed a distinctive lineage sister to all other Laurencia species analyzed. Male plants are described for the first time. This study expands the geographical distribution of L. marilzae to the western Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Geitlerinema amphibium (C. Agardh ex Gomont) Anagn. and G. unigranulatum (Rama N. Singh) Komárek et M. T. P. Azevedo are morphologically close species with characteristics frequently overlapping. Ten strains of Geitlerinema (six of G. amphibium and four of G. unigranulatum) were analyzed by DNA sequencing and transmission electronic and optical microscopy. Among the investigated strains, the two species were not separated with respect to cellular dimensions, and cellular width was the most varying characteristic. The number and localization of granules, as well as other ultrastructural characteristics, did not provide a means to discriminate between the two species. The two species were not separated either by geography or environment. These results were further corroborated by the analysis of the cpcB- cpcA intergenic spacer (PC-IGS) sequences. Given the fact that morphology is very uniform, plus the coexistence of these populations in the same habitat, it would be nearly impossible to distinguish between them in nature. On the other hand, two of the analyzed strains were distinct from all others based on the PC-IGS sequences, in spite of their morphological similarity. PC-IGS sequences indicate that these two strains could be a different species of Geitlerinema. Using morphology, cell ultrastructure, and PC-IGS sequences, it is not possible to distinguish G. amphibium and G. unigranulatum. Therefore, they should be treated as one species, G. unigranulatum as a synonym of G. amphibium. [ABSTRACT FROM AUTHOR]

The genetic and morphological variability among 15 Brazilian strains of Microcystis aeruginosa (Kütz.) Kütz. collected from four locations was examined and compared with several reference strains of M. aeruginosa, M. viridis (A. Br.) Lemm. and M. wesenbergii (Kom.) Kom. in Kondr. Brazilian strains were classified by morphological features and by comparison of the nucleotide sequences of the cpcBA intergenic spacer and flanking regions. Our results indicate that Brazilian strains classified as M. aeruginosa are phylogenetically diverse compared with reference strains of M. aeruginosa and that the current taxonomy underestimates genetic diversity within M. aeruginosa. The data also demonstrate that morphological criteria alone are inadequate to characterize Microcystis species. Although colonial characters were shown to vary considerably in culture, some genetic lineages demonstrated consistent cellular diameter ranges, indicating that cell size has value as a taxonomic character. The detection of six M. aeruginosa genotypes in a single water body indicates that morphological approaches can also seriously underestimate the diversity of Microcystis bloom populations. [ABSTRACT FROM AUTHOR]

Cryptophytes are a small group of photosynthetic biflagellate organisms distributed worldwide in fresh, brackish and marine waters. Although members of this class are easily distinguished from other groups, species identification is difficult and studies concerning their diversity are scarce. Two strains of an undescribed Hemiselmis species were isolated from the marine waters off Brazil and Japan. Analyses of morphology, phycobiliprotein spectral characterization, molecular phylogeny and ITS2 secondary structure comparisons were performed to assist the identification. The morphological features of Hemiselmis aquamarina sp. nov. matches that of other species from the same genus, but it has a new type of phycocyanin. Molecular phylogeny and ITS2 secondary structure support H. aquamarina as a distinct species. Furthermore, phylogenetic inferences indicate H. aquamarina as closely related to H. tepida, H. andersenii and H. rufescens. Currently, all Hemiselmis species have been described from the Northern Hemisphere and most from the subtropical region. H. aquamarina is the first species of this genus described from the South Atlantic. [ABSTRACT FROM AUTHOR]

Latitudinal diversity gradients have provided many insights into species differentiation and community processes. In the well‐studied intertidal zone, however, little is known about latitudinal diversity in microbiomes associated with habitat‐forming hosts. We investigated microbiomes of Fucus vesiculosus because of deep understanding of this model system and its latitudinally large, cross‐Atlantic range. Given multiple effects of photoperiod, we predicted that cross‐Atlantic microbiomes of the Fucus microbiome would be similar at similar latitudes and correlate with environmental factors. We found that community structure and individual amplicon sequencing variants (ASVs) showed distinctive latitudinal distributions, but alpha diversity did not. Latitudinal differentiation was mostly driven by ASVs that were more abundant in cold temperate to subarctic (e.g., Granulosicoccus_t3260, Burkholderia/Caballeronia/Paraburkholderia_t8371) or warm temperate (Pleurocapsa_t10392) latitudes. Their latitudinal distributions correlated with different humidity, tidal heights, and air/sea temperatures, but rarely with irradiance or photoperiod. Many ASVs in potentially symbiotic genera displayed novel phylogenetic biodiversity with differential distributions among tissues and regions, including closely related ASVs with differing north‐south distributions that correlated with Fucus phylogeography. An apparent southern range contraction of F. vesiculosus in the NW Atlantic on the North Carolina coast mimics that recently observed in the NE Atlantic. We suggest cross‐Atlantic microbial structure of F. vesiculosus is related to a combination of past (glacial‐cycle) and contemporary environmental drivers. [ABSTRACT FROM AUTHOR]

[Display omitted] • We present robustly supported and mutually congruent plastid and mitochondrial phylogenies of the genus Hypnea. • Molecular and morphological comparisons of historic and modern collections allowed proposing three new Hypnea species. • Gene losses, InDels and inversions characterize inner clades in Hypnea and Cystocloniaceae. • We obtained complete organellar genomes from the oldest successfully sequenced specimen of Florideophyceae to date. Cystocloniacae is a highly diverse family of Rhodophyta, including species of ecological and economic importance, whose phylogeny remains largely unresolved. Species delimitation is unclear, particularly in the most speciose genus, Hypnea , and cryptic diversity has been revealed by recent molecular assessments, especially in the tropics. Here, we carried out the first phylogenomic investigation of Cystocloniaceae, focused on the genus Hypnea , inferred from chloroplast and mitochondrial genomes including taxa sampled from new and historical collections. In this work, molecular synapomorphies (gene losses, InDels and gene inversions) were identified to better characterize clades in our congruent organellar phylogenies. We also present taxon-rich phylogenies based on plastid and mitochondrial markers. Molecular and morphological comparisons of historic collections with contemporary specimens revealed the need for taxonomic updates in Hypnea , the synonymization of H. marchantiae to a later heterotypic synonym of H. cervicornis and the description of three new species: H. davisiana sp. nov., H. djamilae sp. nov. and H. evaristoae sp. nov. [ABSTRACT FROM AUTHOR]

Abstract: The culture and physiology of red macroalgae calluses are well documented. To date, however, no report has either performed a cytochemical analysis or characterized the ultrastructural organization of calluses at different stages of development and under the effect of plant growth regulators. Therefore, to undertake such analyses, this work studied the red seaweed Gracilariopsis tenuifrons (Bird et Oliveira) Fredericq et Hommersand. Morphology studies suggested three types of calluses: a) terminal callus having an irregular amorphous shape and filamentous projections originating from the cortical region of the thallus; b) apical callus growing on apical branches and having an elongated semispherical shape; and c) intercalary callus developing along the intermediary region of the thallus and having the appearance of small declivities with irregular edges. The abundance of intercalary calluses over terminal and apical calluses is most likely a result of a major cortical surface that would support the cellular growth required to generate calluses. Callus development was initially observed as a matrix of cellular disorganization with filamentous projections; then, the cellular mass seemed to become more compact with spherical uncolored aspect. The presence of starch grains in the inner part of the explant could be explained by absorption from the culture medium and by proper biosynthesis during callus development. Cell wall reaction to staining suggested cellulose and agar composition with acidic polysaccharides. Results suggest that none of the three morphological types of calluses showed any significant differences on the basis of either cytochemistry or ultrastructural organization. [Copyright &y& Elsevier]