Planothidum audax sp. nov. (Bacillariophyta, Achnanthidiaceae), a new diatom from temporary streams in southern Portugal

Abstract

The genus Punctastriata D.M.Williams & Round (1988: 278) contains species that are difficult to identify under light microscopy (LM) (Wetzel & Ector 2021). Their striae are composed of several rows of minute areolae that open interiorly into a single depression. It is the shadow created by this depression under LM that closely resembles the striae in species of Staurosirella D.M.Williams & Round (1988: 274); striae that are often said to have a punch hole appearance (Morales & Manoylov 2006). Thus, scanning electron microscopy (SEM) is often required to confirm the presence of a species of Punctastriata in a sample. Besides the typical multiseriate striae, produced by the formation of multiple viminules in the entire striae (both of these are the defining feature of the genus), the species share all the remaining features with other small araphid genera lacking a rimoportula, such as the already mentioned Staurosirella, but also Nanofrustulum Round, Hallstainsen & Paasche (1999: 345), Opephora P.Petit (1888: 130–131), Pseudostaurosira D.M.Williams & Round (1988: 276), Pseudostaurosiropsis E.Morales (2001: 116), Sarcophagodes E.Morales (2002: 111), Stauroforma R.J.Flower, Jones & Round (1996: 53), and Staurosira Ehrenberg (1843: 45) (see table 1 in Morales et al. 2019). To date, nine species have been included in Punctastriata (see table 1 in Wetzel & Ector 2021). These have been reported from around the globe, but by our own finding, it appears that new species can still be found, even in areas that have previously received attention. This is the case of temporary streams in southern Portugal, ecosystems with dynamic benthic communities, even in the dry period, when diatoms persist in the stream beds in reduced, shallow pools or as dry biofilms (Novais et al. 2020).