This paper is a contribution to the morphological and molecular characterization of the cyanobacterium Brasilonema robertilamii from populations found in Central Mexico. The general growth form and the morphological, morphometric and ecological characteristics of the populations studied clearly correspond to those described for Brasilonema roberti-lamii (basionym: Tolypothrix roberti-lamii) from the French Antilles. Based on molecular data from DNA sequencing of the16S rRNA gene and the IGS of the cpcB-cpcA phycocyanin operon (cpcBA-IGS), we propose that the populations that we studied are closely related to those of other Brasilonema species, including B. octagenarum UFV-OR1, UFV-E1 and HA4187-MV1-p1F, Brasilonema sennae CENA 114, B. tolantongensis, B. terrestre CENA 116, B. angustatum HA4187-MV1-B2+p1F and HA4187-MV1-B2+p1H and B. bromeliae SPC951. Our findings support the transference of Tolypothrix roberti-lamii, which was made based exclusively on morphological criteria, to Brasilonema. The use of molecular analyses in addition to traditional morphological and ecological criteria, known as polyphasic approach, is a good alternative to describe taxa of cyanobacteria, mainly at the genus and species levels.

New approaches in taxonomy and the introduction of molecular tools have substantially changed the taxonomy of cyanobacteria, leading to new genera and species being defined based on genetic and morphological investigations. In addition, molecular tools have confirmed several previously defined cyanobacteria genera, including some based on morphological and ecological features. Several of them have also been split into new generic entities, such as Brasilonema. In the central region of Mexico, several populations have been identified to share some traits with this new genus. In the region of Tolantongo, Hidalgo (Hgo), we found cyanobacteria populations that correspond to Brasilonema description (Fiore et al. 2007), however the development of trichomes and hormogonia did not agree with the diagnosis of Brasilonema. We describe and analyze the cyanobacteria populations that we found in Tolantongo, and compare their features with the diagnostic generic features and those of several Brasilonema species. The results of morphological analyses were tested using molecular phylogenetic data derived from 16S RNA gene sequencing and the use of marker cpcBA-IGS for phycocyanin operon. From our analyses we conclude that the strain from Tolantongo belongs to the genus Brasilonema, and the differences observed are sufficient to propose a new species.

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