Distribution, morphology and ecological niche of <i>Batrachospermum</i> and <i>Sheathia</i> species (Batrachospermales, Rhodophyta) in the <i>fontanili</i> of the Po plain (northern Italy)

<div><p></p><p>Twenty-three freshwater springs of the Po plain (northern Italy) were surveyed and visited multiple times during 2011–2013 to assess water quality and algal taxa present. Despite poor water conditions of this human-altered floodplain, a relatively high number of taxa referable to the freshwater red algae, <i>Batrachospermum</i> and <i>Sheathia</i>, were observed. The identity of specimens collected was based on morphology and confirmed with sequence data. The specimens belonged to <i>Sheathia arcuata, S. boryana, Batrachospermum atrum, B. gelatinosum</i> and <i>B. gelatinosum</i> f. <i>spermatoinvolucrum</i>. This is the first report of <i>B. gelatinosum</i> f. <i>spermatoinvolucrum</i> outside North America. Niche analysis revealed a marked difference in the physical and chemical preferences of the freshwater red algae recorded. The occurrence of <i>S. boryana</i> was limited to relatively low nitrate and higher oxygen concentrations. Conversely, the spatial distribution of the other four taxa indicated that they were able to tolerate high concentrations of nitrate (up to 53.6 mg l<sup>–1</sup>) and low rates of dissolved oxygen saturation (as low as 3%). All the specimens of <i>B. gelatinosum</i> collected had few to many trichogynes deformed by a basal protuberance or knob, a structure previously unobserved in this species. No other taxa showed any deformities. The ecological analyses confirmed the existence of a relationship between the environmental conditions of the springs and the occurrence of knobs.</p></div>