Aulacoseira alpigena (Grunow) Krammer (fig. 2b)*

Aulacoseira ambigua (Grunow) Simonsen (fig. 2a)*

Aulacoseira distans (Ehrenb.) Simonsen (fig. 2c)

Cyclotella meneghiniana Kütz. (fig. 2e)

Discostella stelligera (Cleve & Grunow) Houk & Klee (fig. 2f)

Melosira varians C.Agardh (fig. 2d)

Asterionella formosa Hassall (fig. 2r)

Diatoma mesodon (Ehrenb.) Kütz. (fig. 2s)

Diatoma vulgaris Bory (fig. 2t)

Fragilaria bidens Heib. (fig. 2j)

Fragilaria capucina var. capitellata (Grunow) Lange-Bert. (fig. 2g)

Fragilaria capucina var. capucina Desm. (fig. 2i)

Fragilaria capucina var. rumpens (Kutz.) Lange-Bert. (fig. 2h)

Fragilaria capucina var. vaucheriae (Kütz.) Lange-Bert. (fig. 2m)

Fragilaria crotonensis Kitton (fig. 2q)

Fragilaria parasitica (W.Sm.) Grunow (fig. 2k) *

Fragilariforma virescens (Ralfs) D.M. Williams & Round (fig. 2l)

Hannaea arcus (Ehrenb.) R.M.Patrick (fig. 2n)

Meridion circulare var. constrictum (Ralfs) Van Heurck (fig. 2v)

Tabellaria floculosa (Roth.) Kütz. (fig. 2u)

Ulnaria biceps (Kütz.) Compère (fig. 2o)*

Ulnaria ulna (Nitzsch) Compère (fig. 2p)

Achnantes brevipes var. intermedia (Kütz.) Cleve (fig. 4o)*

Achnanthes subhudsonis Hust. (fig. 4l)

Achnanthidium minutissimum (Kütz.) Czarneki (fig. 4m)

Achnanthidium subatomus (Hust.) Lange-Bert. (fig. 4n)

Amphora inaeriensis Krammer (fig. 9n)*

Amphora ovalis (Kütz.) Kütz. (fig. 9m)

Amphora pediculus (Kütz.) Grunow (fig. 9o)

Bacillaria paradoxa J.F.Gmel. (fig. 10a)*

Brachysira intermedia (Østrup) Lange-Bert. (fig. 5a)

Brachysira neglectissima Lange-Bert. (fig. 5c)

Brachysira neoexilis Lange-Bert. (fig. 5b)

Caloneis bacillum (Grunow) Cleve (fig. 6b)

Caloneis molaris (Grunow) Krammer (fig. 6c)

Caloneis silicula (Ehrenb.) Cleve (fig. 6d)

Cavinula variostriata (Krasske) D.G.Mann & Stickle (fig. 5d) *

Cocconeis pediculus Ehrenb. (fig. 4r)

Cocconeis placentula var. euglypta (Ehrenb.) Grunow (fig. 4p)

Cocconeis placentula var. lineata (Ehrenb.) Van Heurck (fig. 4q)

Cocconeis placentula var. pseudolineata Geitler (fig. 4s)

Craticula buderi (Hust.) D.G.Mann (fig. 8 h)*

Cymbella aspera (Ehrenb.) Cleve (fig. 8 k)

Cymbella tumida (Bréb.) Van Heurck (fig. 8 j)

Diploneis elliptica (Kütz.) Cleve (fig. 5n)

Diploneis oculata (Bréb.) Cleve (fig. 5o)

Diploneis ovalis (Hilse) Cleve (fig. 5m)

Encyonema gracile Rabenh. (fig. 8 m)

Encyonema minutum (Hilse) D.G.Mann (fig. 8i)

Encyonema silesiacum (Bleisch) D.G.Mann (fig. 8l)

Eunotia bilunaris (Ehrenb.) Mills (fig. 3a)

Eunotia exigua (Breb. ex Kütz.) Rabenh. (fig. 3e)

Eunotia faba Ehrenb. (fig. 3c)

Eunotia formica Ehrenb. (fig. 3b)

Eunotia implicata Nörpel, Lange-Bert. & Alles (fig. 3f)

Eunotia incisa W.Greg. (fig. 3g)

Eunotia intermedia (Krasske ex Hust.) Nörpel & Lange-Bert. (fig. 3j)

Eunotia minor (Kütz.) Grunow (fig. 3i)

Eunotia pectinalis var. undulata (Ralfs) Rabenh. (fig. 3k)

Eunotia praerupta Ehrenb. (fig. 3l)

Eunotia soleirolli (Kutz.) Rabenh. (fig. 3m)*

Eunotia subarcuatoides Alles, Norpel & Lange-Bert. (fig. 3n)

Frustulia amphipleuroides (Grunow) Cleve (fig. 5h)

Frustulia saxonica Rabenh. (fig. 5i)

Frustulia vulgaris (Thwaites) De Toni (fig. 5j)

Gomphonema acuminatum Ehrenb. (fig. 9a)

Gomphonema angustum C.Agardh (fig. 9k)

Gomphonema gracile Ehrenb. (fig. 9d)

Gomphonema ibericum E.Reichardt (fig. 9b)

Gomphonema minutum (C.Agardh) C.Agardh (fig. 9e)

Gomphonema parvulum var. parvulum (Kütz.) Kütz. (fig. 9g)

Gomphonema parvulum var.exilissimum Grunow (fig. 9f)

Gomphonema pseudoaugur Lange-Bert. (fig. 9h) **

Gomphonema pumilum (Grunow) Reichardt & Lange-Bert. (fig. 9i)*

Gomphonema rhombicum M.Schmidt (fig. 9j)

Grunowia solgensis (Cleve-Euler) Aboal (fig. 11e)

Gyrosigma acuminatum (Kutz.) Rabenh. (fig. 8a)*

Hantzschia amphioxys (Ehrenb.) Grunow (fig. 11c)

Hippodonta capitata (Ehrenb.) Lange-Bert., Metzeltin & Witkowski (fig. 8g)

Humidophila contenta (Grunow) Lowe, Kociolek, J.R.Johansen, Van de Vijver, Lange-Bert. & Kopalová (fig. 5e)

Humidophila perpusilla (Grunow) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bert. & Kopalová (fig. 5g)

Humidophila laevissima (Cleve) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bert. & Kopalová (fig. 5f)*

Iconella biseriata (Bréb.) Ruck & Nakov (fig. 11l)

Iconella helvetica (Brun) Ruck & Nakov (fig. 11k)

Iconella linearis (W.Sm.) Ruck & Nakov (fig. 11j)

Karayevia oblongella (Østrup) Aboal (fig. 4a)

Kolbesia suchlandtii (Hust.) Kingston (fig. 4b)

Lemnicola hungarica (Grunow) Round & Basson (fig. 4c)

Luticola goeppertiana (Bleisch) D.G.Mann (fig. 5l)

Navicula angusta Grunow (fig. 7e)

Navicula clementis Grunow (fig. 7c)*

Navicula concentrica Carter (fig. 7a)

Navicula cryptocephala Kütz. (fig. 7f)

Navicula cryptotenella Lange-Bert. (fig. 7g)

Navicula cryptotenelloides Lange-Bert. (fig. 7h)

Navicula gregaria Donkin (fig. 7k)

Navicula lanceolata (C.Agardh) Ehrenb. (fig. 7b)

Navicula minima Grunow (fig. 7i)

Navicula rhyncocephala Kütz. (fig. 7j)

Navicula rostellata Kütz. (fig. 7m)

Navicula tripunctata (O.F.Müll.) Bory (fig. 7l)

Naviculadicta langebertalotii Cantonati & Leira (fig. 12)***

Neidium affine (Ehrenb.) Pfitzer (fig. 5k)

Nitzschia amphibia Grunow (fig. 10c)

Nitzschia archibaldi Lange-Bert. (fig. 10e)

Nitzschia dissipata (Kütz.) Grunow (fig. 10i)

Nitzschia fonticola Grunow (fig. 10h)

Nitzschia inconspicua Grunow (fig. 10g)

Nitzschia nana Grunow (fig. 11b)

Nitzschia palea (Kütz.) W.Sm. (fig. 10k)

Nitzschia palea var. debilis (Kütz.) Grunow (fig. 10f)

Nitzschia recta Hantzsch (fig. 10l)

Nitzschia sp. (fig. 10b)

Nupela lapidosa (Krasske) Lange-Bert. (fig. 4d)

Peronia erinacea Bréb. & Arn. (fig. 3o)

Pinnularia parvulissima Krammer (fig. 6f)

Pinnularia acrosphaeria W.Sm. (fig. 6o)

Pinnularia borealis var. sublinearis Krammer (fig. 6m)

Pinnularia divergens W.Sm. (fig. 6e)***

Pinnularia lundii Hust. (fig. 6k)

Pinnularia sinistra Krammer (fig. 6i)***

Pinnularia stidolphii Krammer (fig. 6p)**

Pinnularia subcapitata W.Greg. (fig. 6h)

Planothidium daui (Foged) Lange-Bert. (fig. 4e)

Planothidium lanceolatum (Bréb. ex Kütz.) Lange Bert. (fig. 4f)

Planothidium peragalli (Brun & Héribaud) Round & Bukht. (fig. 4g)*

Psammothidium helveticum (Hust.) Bukht. & Round (fig. 4h)

Psammothidium subatomoides (Hust.) Bukht. & Round (fig. 4i)

Reimeria sinuata (W.Greg.) Kociolek & Stoermer (fig. 9p)

Rhoicosphenia abbreviata (C.Agardh) Lange-Bert. (fig. 8f)

Sellaphora pupula (Kütz.) Mereschk. (fig. 6a)

Stauroneis anceps Ehrenb. (fig. 8c)

Stauroneis kriegerii Ehrenb. (fig. 8d)

Stauroneis obtusa Lagerst. (fig. 8e)

Stauroneis prominula (Grunow) Hust. (fig. 8b)*

Iconella delicatissima (F.W.Lewis) Ruck & Nakov (fig. 11f)

Surirella angusta Kütz (fig. 11g)

Surirella brebissonii Krammer & Lange-Bert. (fig. 11o)

Surirella patella Kutz. (fig. 11m)

Surirella roba L.Leclercq (fig. 11h)

Surirella robusta Ehrenb. (fig. 11i)

Achnanthes intermedia Kütz., Alg. Aq. Dulc. Germ. 3: 3 (1833).

Achnanthes subsessilis Kütz., Alg. Aq. Dulc. Germ. 5: 3 (1833).

Habitat and distribution.—This species has a cosmopolitan distribution along lowland areas even in estuaries. Hustedt (1930) thought that it could be regarded as caused by reduced salinity variation.

Note.—A similar taxon is Achnanthes taylorensis D.E.Kellogg, Stuiver, T.B.Kellogg & G.H.Denton which has been often confused with Achnanthes brevipes var. intermedia. However, both differ in striae density (13–15 vs. 10 in 10 μm; Cleve 1895).

Habitat and distribution.—Characteristic habitats are oligotrophic to dystrophic waters with very low electrolyte content on silicate soils, particularly in mountainous areas.

Note.—A similar taxon is Brachysira brebissonii R.Ross, but differs because of the duller, broader and not early narrowing ends. The distribution of this taxon in Europe is not known precisely because of the confussion with Brachysira brebissonii.

Frustulia gastroides Kütz., Linnaea 8(5): 543, pl.13 fig.9 (1833); Cymbella gastroides (Kütz.) Bréb. & Godey, Mém. Soc. Acad. Sci. Falaise.: 49 (1835); Cymbella gastroides (Kütz.) Kütz., Kieselschal. Bacill.: 79, pl. 6 fig. 4B (1844), comb. superfl.

Habitat and distribution.—Although widely distributed in Europe, it is not often recorded in large numbers. It prefers oligotrophic waters, especially favoured are habitats in the mountains of average electrolyte content.

Note.—It is distinguished from other similar taxa by outline, size, pearl-like puncta, and especially by the structure of the proximal raphe ends. Cymbella aspera has large roundish central pores, whereas Cymbella lanceolata (C.Agardh) C.Agardh has crosier-shaped central fissures. The puncta of Cymbella neogena (Grunow) Krammer are less shining “aspera”, and this taxon has more than 12 puncta/10 μm, and the central pores are less distantly arranged. The valves of Cymbella peraspera Krammer are larger —broader than 38 μm—. Cymbella subaspera Krammer is smaller, the outline is stockier and smaller forms have straight to slightly concave ventral margins.

Habitat and distribution.—In Europe Eunotia faba was found in Ireland, Wales and Romania from soft, somewhat dystrophic ponds, lakes and swamps. Camburn & Charles (2000) reported this taxon —as Eunotia vanheurckii R.M.Patrick— from low-alkalinity lakes in the Adirondack Mountains of New York. Eunotia faba has been recorded from in anthropogenically undisturbed oligotrophic, weakly acidic to alkaline habitats in mountainous areas (Lange-Bertalot & al. 2011).

Note.—A similar taxon is Eunotia incisa that has acutely rounded apices and narrower valves —less than 5 μm wide—. Eunotia rhomboidea Hustedt is also heteropolar, or asymmetric to the transverse axis, but Eunotia faba has distinctly wider valves.

Eunotia impressa var. angusta Grunow in Van Heurck, Syn. Diatom. Belgique, Atlas, pl. 33 fig. 22, pl. 35 fig.1 (1881).

Habitat and distribution.—This taxon is fairly common in silicate-dominated streams of the highlands and the North German lowlands, occurring even at high numbers, but rarely observed in stagnant water (Hoffman & al. 2013). The habitats are largely anthropogenically undisturbed, low in electrolytes and oligotrophic to dystrophic. Ortiz-Lerín & Jaume Cambra (2007) reported this taxon from low to upland streams in Northern Spain —76–1,356 m a.s.l.— with pH = 4.3‒7.9 and conductivity ranging from 4.17 to 720 μS∙cm^-1. Eunotia implicata is an acidophilus taxon, mainly occurring at pH below 7 (Van Damm & al. 1994). In this work Eunotia implicata has a pH optimum of 6.3 and was found in oligotrophic lowland streams.

Note.—Eunotia implicata can be mistaken with exceptionally thin specimens of Eunotia minor (Kütz.) Grunow, but are distinguished by a higher striae density —9‒16/10 μm— in the middle section.

Habitat and distribution.—It is one of the most common Eunotia species in Europe, probably a cosmopolitan species. Common in various electrolyte-poor, oligotrophic to dystrophic waters. Abundant in streams of the low mountain ranges of the study area but rare in the lowlands. Common in acidic, freshwater environments with low levels of organic matter and nutrients, and weakly mineralized. Occasionally it can occur in high abundances. In the north of Spain this species was found in habitats with pH 4.7‒6.8, conductivity 4.17‒194 μS∙cm^-1, although reached its maximum abudance at pH 5.3‒6, conductivity 38‒51 μS∙cm^-1, and altitude 472‒484 m a.s.l. (Ortiz-Lerín & Cambra 2007). In our study pH optimum was 6.3 and ranged between 5.5 and 6.8.

Note.—Several forms and variations in length, width, and stria density are currently included in the broad concept of Eunotia incisa. Lange-Bertalot & al. (2011) have further described new species from Europe, such as Eunotia incisadistans Lange-Bert. & Sienkiewicz, which has broader valves with lower stria density. Eunotia incisa is also similar to Eunotia boreoalpina Lange-Bert. & Nörpel-Schempp and Eunotia rhomboidea Hust. only in girdle view. Eunotia veneris (Kütz.) De Toni was often confused in the older literature and is not detected in Central Europe. Valves of Eunotia incisa, however, are symmetric in regard to apex width and position of the helictoglossae compared to the asymmetry in these features in Eunotia rhomboidea. In North America, more differentiable taxa occur. Eunotia incisa is similar to Eunotia canicula P.C.Furey, R.L.Lowe & J.R.Johans. and the size range of the two species overlap. The apices of Eunotia incisa, however, are more nose-like than the apices of Eunotia canicula. Furthermore, the valves of Eunotia canicula are narrower and the helicotoglossae are closer to the apex —less inset— as compared to Eunotia incisa. Individuals such as those in fig. 61 that have broader and rounded apices, such as valves with morphology similar to Taf. 161 figs. 13‒15 in Krammer & Lange-Bertalot (1991) could be considered as a new species, although for the moment they should be considered only as another variation of valve morphology.

Habitat and distribution.—Spread, so far known with certainty only from the northern hemisphere, scattered in the area, mostly occurring in poor populations. Ortíz-Lerín & Cambra (2007) found this taxon in habitats with pH 5.4‒7.3, and low conductivity —17.6‒112 μS∙cm^-1— in mid-altitude sites —205‒1,086 m a.s.l.—. Acidophilus, mainly occurring at pH below 7 (Van Damm & al. 1994). In the studied area the species has a pH optimum of 6.2.

Note.—Similar outline to Eunotia faba. However the location of the terminal nodes is different.

Habitat and distribution.—This taxon is not very well represented in this region, it was found only in six sites with low abundance. Often in circumneutral to weakly acidic, low conductivity waters (Patrick & Reimer 1966).

Note.—This variety of Eunotia pectinalis has many, slight undulations along the dorsal margin and a central swelling to the ventral margin. These characters are used to distinguish the variety Eunotia pectinalis var. undulata from its nominate variety (Patrick & Reimer 1966; Krammer & Lange-Bertalot 1991).

Eunotia praerupta var. curta Grunow, Syn. Diatom. Belgique, pl. 34 (1881); Eunotia praerupta f. curta (Grunow) A.Cleve, Bih. Kongl. Svenska Vetensk.-Akad. Handl. 21: 33 (1895); Eunotia praerupta f. curta (Grunow) Mayer, Denkschr. Königl.-Baier. Bot. Ges. Regensburg. I: pl. 2, fig.11 (1917), comb. superfl.; Eunotia praerupta-monos var. curta (Grunow) Cleve-Euler, Acta Geogr. 10(1): 16 (1948); Eunotia praemonos var. curta (Grunow) Cleve-Euler, Kongl. Svenska Vetensk.-Akad. Handl. ser. IV, 4(1): 115, fig. 452v (1953). Fig. 3l.

Habitat and distribution.—Usually in mountainous localities in acid to circumneutral waters (Patrick & Reimer 1966). Acidophilus: mainly occurring at pH < 7 (Van Damm & al. 1994).

Note.—This species can be easily recognized by the convexity of the dorsal margin and by the characteristic truncate-rostrate to slightly capitate ends.

Habitat and distribution.—It is a common diatom in Galicia rivers occuring in high abundance. Its highest abundance was at pH 6.1. Eunotia subarcuatoides has been classified as an acidobiontic with an optimal occurrence at pH < 5.5 (Van Damm & al. 1994). Anyway, it seems to tolerate high and strong variations of pH values (Alles & al. 1991; Ortiz-Lerín & Cambra 2007).

Habitat and distribution.—This is a characteristic species from dystrophic and low-electrolyte waters. Indicator of high ecological quality.

Note.—Frustulia crassinervia (Bréb.) Lange-Bert. & Krammer has prominently undulate valve margins, while the margins of Frustulia inculta P.Siver, J.Pelczar & P.Ham. are very slighty undulate. In addition, the valve margins of Frustulia crassinervia are more strongly undulate and its apices more narrowly protracted than those in Frustulia saxonica.

Navicula flotowii Grunow, Syn. Diatom. Belgique: 109, pl. 14 fig. 41 (1880); Navicula perpusilla var. flotowii (Grunow) J.B.Petersen, Bot. Iceland. 2(2): 328‒447 (1928).

Habitat and distribution.—Humidophila perpusilla is a widespread diatom common in silicate dominated waters in highlands. It has also been cited from aerial habitats and often occurring in association with Diadesmis contenta (Grunow) D.G.Mann. Characteristic are also habitats with reduced light intensity such as caves and rock crevices. The freshwater genus Humidophila Lowe & al. is typically restricted to subaerial habitats (Round & al. 1990). In our study, Humidophila perpusilla was found in poor electrolyte, circumneutral and oligotrophic waters.

Note.—The complex of species around Diadesmis contenta s.l. was reviewed in part by Moser & al. (1998). Lowe & al. (2014) proposed the genus Humidophila to accommodate a number of taxa formerly classified within the subgenus Paradiadesmis Lange-Bert. & Le Cohu. Based on valve morphology analyses with scanning electron microscopy and microhabitat preferences, Diadesmis perpusilla was transferred to Humidophila. Our specimens most closely resemble Humidophila perpusilla as illustrated in Krammer & Lange-Bertalot (1986) as Navicula gallica var. perpusilla.

Habitat and distribution.—The type locality —Soutomaior, at the River Verdugo— is a low altitude —140 m a.s.l.— stream stretch located in a narrow valley with steep slopes. The river bed is dominated by hard geological substrata, such as granites and phyllites. This species is typical of low-conductivity, meso-eutrophic, slightly-acidic but non-acidified, running-water sites, that reaches maximum relative abundances in autumn.

Note.—The most similar Navicula s.l. species are Navicula natchikae J.B.Petersen and Navicula oregonensis Hustedt. Both are clearly larger, and have parallel straight margins. Striae are interrupted close to the valve margin by a longitudinal rib developing parallel to the valve margin.

Habitat and distribution.—Pinnularia divergens was found at five study sites: the Ouro, Sor, Eume, Traba, and Sar rivers. All of the sites are oligotrophic waters from mountainous areas with a pH below 7 and low-electrolyte content.

Note.—At least eleven varieties exist in the literature, though some of these merely represent life-cycle stages. Striae divergence criterion, bayonet-shaped terminal fissures, and conical spots in the small fascia are important characters (Krammer 2000).

Habitat and distribution.—Specimens were found at the Furelos river. The Furelos river is a tributary of the Ulla on its right bank. The river is located in the southeast corner of the province of A Coruña —belonging to Terra de Melide—, almost in the center of Galicia, and it flows through ultramafic rocks —the largest outcrop in the Iberian northwest—. The site is located at medium altitude —700 m a.s.l. — at 25 km from the source with an upstream drainage area of 150 km². Pinnularia sinistra was found when the stream was at high flow condition. Pinnularia sinistra is cosmopolitan in the palaearctic region. Very common and locally abundant in oligotrophic electrolyte-poor, acidic streams. Tolerant to anthropogenic acidification (Hoffmann & al. 2011).

Habitat and distribution.—Pinnularia stidolphii was found in Traba and Ulla rivers. The Traba river is situated in a landscape dominated by granitic rocks. The study site was located at low altitude —18 m a.s.l.—, at 14 km from the river source and a catchment area of 6.5 km². The Ulla river runs through granites in contact with schists and basic rocks. The study site is also situated at low altitude —64 m a.s.l.—, 96 km downstream of its source. Industrial activities and urban development are the main impacts, respectively. Probably abundant species in temperate regions of North and South Hemisphere, in waters poor in organic matter.

Habitat and distribution.—The habitat is not clearly defined as a result of the problematic distinction from Planothidium granum (M.H.Hohn & Hellerman) Lange-Bert. Uncommon in Galicia rivers and streams, relatively abundant (> 5%) at only one site, poor in organic content at pH close to neutral, with a rather low mineralization.

Note.—Often confused with Planothidium granum, but Planothidium daui has clearly beak-like to capitate apices and more linear valve edges.

Habitat and distribution.—Cosmopolitan species but rare. Mostly observed sporadically in oligotrophic and dystrophic acids waters of siliceous mountain regions, well-oxygenated and low in organic matter and nutrients. Indicator of high ecological quality.

Note.—Based on phylogenetic analyses along with morphological studies Ruck & al. (2016) have recently reclassified the Surirellales and proposed the transfer of Surirella delicatissima into a new monotypic genus, Iconella Jurilj.

Habitat and distribution.—Iconella linearis is considered a cosmopolitan species, common in slightly acidic to neutral pH, weakly to moderately mineralized and moderately impacted by organic matter and nutrients.

Note.—Also transferred into genus Iconella by Ruck & al. (2016). Very similar to Surirella roba Leclercq but Iconella linearis has a larger size and coarser structure, with more distantly spaced fibulae and corrugations.