Gomphonema acidoclinatiforme (Gomphonemataceae, Bacillariophyta) in Brazil: fine morphology and distribution of a rarely reported diatom

This study provides the first record of Gomphonema acidoclinatiforme in Brazil, a species previously known only from its type locality in Madagascar. Specimens were observed in four major Brazilian regions: North, Southeast, Central-West, and South. Gomphonema acidoclinatiforme is readily distinguishable by its asymmetrical rhombo-lanceolate to lanceolate valves with slight central inflation and pronounced curvature, a single rounded stigmoid, thickened terminal raphe nodules, and, in the SEM, striae confined within alveoli lacking silica struts and a basal pore field restricted to the valve mantle. Comparisons with morphologically similar taxa of the G. gracile species complex are presented to refine the taxonomic boundaries of G. acidoclinatiforme. The broader distribution of G. acidoclinatiforme across tropical and subtropical regions of Brazil suggests that the species is more widespread than previously recognized.