Achnanthidium nanum (F.Meister) Novais & Jüttner 2015

Novais, Maria Helena, Jüttner, Ingrid, Vijver, Bart Van De, Morais, Maria Manuela, Hoffmann, Lucien & Ector, Luc, 2015, Morphological variability within the Achnanthidium minutissimum species complex (Bacillariophyta): comparison between the type material of Achnanthes minutissima and related taxa, and new freshwater Achnanthidium species from Portugal, Phytotaxa 224 (2), pp. 101-139 : 121

Achnanthidium nanum (F.Meister) Novais & Jüttner , comb. nov.

Basionym: Achnanthes nana F.Meister, Berichte der Schweizerischen Botanischen Gesellschaft 44: 88, fig. 2. 1935.

Distribution and ecology:— Achnanthes nana was first found in high altitude lakes in the Swiss Alps, Canton of Valais, including the well-known Riffelsee near the Matterhorn. In central and northern Portugal it was found at 12 sites in the Tejo (1 site), Mondego (3 sites), Douro (4 sites), Cávado (2 sites) and Lima (2 sites) watersheds (>1% relative abundance, Fig. 1 ). It dominated the assemblages at six of these sites and reached a maximum relative abundance of 87.5% at Alvoco das Várzeas (Mondego watershed). The Portuguese streams are well oxygenated soft waters with alkalinity values between 5–34 mg CaCO 3 l-1, low calcium concentrations (2–18 mg l-1), low conductivity (36–94 μS cm-1), slightly acidic to slightly alkaline pH (6.1–7.7), and low to medium concentrations of nitrate (0–4270 μg NO 3 - l-1), nitrite (0–10 μg NO 2 - l-1), phosphate (0–52 μg PO 4 3- l-1) and total phosphorus (1–47 μg P l-1, Table 3). In Scotland the species was common and abundant in streams with circumneutral to slightly alkaline pH, low to medium conductivity and alkalinity mostly below 60 mg CaCO 3 mg l-1. In Nepal it was most abundant in streams with calcium concentrations below 15 mg l-1.

In Portugal Achnanthidium nanum was associated with taxa which are known from varied habitats. Achnanthidium caravelense for example is known from circumneutral waters, with low conductivity and relatively low nutrient concentrations ( Novais et al. 2011), while other taxa including Achnanthidium subhudsonis (Hust. 1921: 144) H.Kobayasi in Kobayasi et al. (2006: 129), Cocconeis lineata Ehrenb. (1854: 8) , Encyonema sp. , Eolimna minima (Grunow in Van Heurck 1880: 107) Lange-Bert. in Moser et al. (1998: 153), Fragilaria perminuta (Grunow in Van Heurck 1881: pl. 40, fig. 23) Lange-Bert. in Krammer & Lange-Bertalot (2004: 581), F. cf. socia (N.M. Wallace 1955: 1) Lange-Bert. (1980: 749) , Gomphonema rhombicum M.Schmidt in Schmidt et al. (1904: pl. 248, fig. 1), Karayevia oblongella ( Østrup 1902: 252) Aboal in Aboal et al. (2003: 159), Planothidium lanceolatum (Bréb. ex Kütz. 1846: 247) Lange-Bert. (1999: 287) and Reimeria sinuata (W.Greg. 1856: 4) Kociolek & Stoermer (1987: 457) are regarded as neutrophilous or alkaliphilous, oligohalobous, nitrogen tolerant or N-heterotrophic facultatives and occur over a range of oxygen conditions, saprobity and trophic status ( Van Dam et al. 1994). In Scotland Achnanthidium nanum was also associated with species sensitive and tolerant to nutrient enrichment including A. minutissimum , Fragilaria rumpens (Kütz. 1844: 69) G.W.F. Carlson (1913: 29) , Navicula claytonii J.R. Carter (1987: 633) , N. gregaria Donkin (1861: 10) , N. lanceolata (C. Agardh 1827: 626) Kütz. (1844: 94) , Gomphonema calcifugum Lange-Bert. & E.Reichardt in Lange-Bertalot & Genkal (1999: 53) and G. parvulum Kütz. (1849: 65) . In Nepal Achnanthidium nanum was more often found in unimpacted streams and here associated with A. minutissimum , Diatoma mesodon (Ehrenb. 1839: pl. 2, fig. 9) Kütz. (1844: 47) and Hannaea arcus f. recta (P.T. Cleve 1898: 9) Foged (1981: 61) . Occasionally it was associated with Adlafia minuscula (Grunow in Van Heurck 1880: pl. 14, fig. 3) Lange-Bert. in Lange-Bertalot & Genkal (1999: 32), Cocconeis placentula Ehrenb. (1838: 194) , Encyonema minutum (Hilse in Rabenhorst 1862: n° 1261) D.G.Mann in Round et al. (1990: 667), Gomphonema calcifugum , G. parvulum , Nitzschia dissipata (Kütz. 1844: 64) Grunow (1862: 561) and Reimeria sinuata .

Figures

FIGURE 1. Location of Portuguese Achnanthidium species. White star: A. nanum; white diamond: A. pseudolineare; white square: A. lusitanicum; white circle: A. duriense.