On the identity and distribution in northern Portugal of three gomphonema species currently misidentified as gomphonema clevei

Abstract

Gomphonema specimens with wide axial areas collected from streams in Northern Portugal were examined by light and scanning electron microscopy. Three species were found and identified as G. rhombicum, G. uniserhombicum and G. ibericum. No specimens were found with the features of G. clevei sensu strict, and previous records from the region with the latter name are regarded as representing one or a mixture of the three species examined herein. The three species differed in the fine details of the striae; double alternating poroids in G. rhombicum, slit-like with irregular outlines in G. uniserhombicum and single or divided slit-like poroids in G. ibericum. Differences in size and shape of the valve and axial area allow discrimination of at least medium-sized to large specimens of the three species. Gomphonema rhombicum was the most common species, sometimes occurring as dominant in the epilithon. Both G. uniserhombicum and G. ibericum were found more sparsely and always in communities containing G. rhombicum. All species were found in slightly acidic to circumneutral, well-oxygenated waters with low conductivity, poor in nutrients and with low organic content.