Denticula, Hantzschia and Tryblionella (Bacillariaceae, Bacillariophyta) from northwestern Ceará freshwaters

Abstract Diatoms constitute a representative portion of the algal community of freshwater aquatic environments, but their studies are centered mostly in the south and southern regions of Brazil, making the microalgae biodiversity of water bodies in the semiarid practically unknown. In the state of Ceará, the few records of the Bacillariaceae are centered in the southern region of the state and are generally not identified at specific level. Denticula, Hantzschia, and Tryblionella are worldwide distributed diatom genera that belong to the family Bacillariaceae. The group is characterized by raphe located on a channel, internally supported by silica extensions, the fibulae. This is a taxonomic study on the genera Denticula, Hantzschia, and Tryblionella found in water bodies in northwestern Ceará state. Planktonic and periphytic samples were collected in four hydrographic basins, which are influenced by the semiarid climate, located in northwestern Ceará, northeastern Brazil. Fourteen infrageneric taxa were identified, described, and illustrated, all being pioneer citations for Ceará. The present study highlighted the underestimated diversity of diatoms in the semiarid region of Ceará and the need to cover undersampled or never explored regions to significantly contribute to the knowledge of the diatom flora and its distribution in Brazilian aquatic environments.