Brachysira garrensis (Lange-Bertalot & Krammer) Lange-Bertalot, 1994
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https://doi.org/ 10.11646/phytotaxa.326.1.1 |
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https://treatment.plazi.org/id/03EECE1F-4E6A-FFF0-01EA-F9E1FA98A760 |
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Felipe |
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Brachysira garrensis (Lange-Bertalot & Krammer) Lange-Bertalot |
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Brachysira garrensis (Lange-Bertalot & Krammer) Lange-Bertalot ( Figs 111–135 View FIGURES 111–135 )
This taxon is distinguished from B. microcephala in LM by the denser striae. Krammer & Lange-Bertalot (2000) proposed that the finer structure, including stria density (≥ 36 in 10 μm) and lack of protracted apices can be used to differentiate B. garrensis . A higher stria density for some populations of B. microcephala reported in this study (see below, but also in Compère 1988) and the fact that rostrate-subcapitate valves may occur in both taxa confirms a greater overlap in these characteristics for Irish populations at least (compare Figs 133 & 135 View FIGURES 111–135 with 171 & 172). Nevertheless, the higher average stria density and the “finer-appearing pattern” of areolae, which were not observable or are more difficult to resolve in B. garrensis relative to B. microcephala , was sufficiently reliable to enable their separation. Some challenging material included diminutive rhombic forms of both species which often co-occur (compare Figs 125–126 View FIGURES 111–135 & Figs 160–165 View FIGURES 136–172 ) and smaller capitate valves of B. microcephala with dense striae ( Figs 129 View FIGURES 111–135 , 244–246 View FIGURES 240–252 ). Valve dimensions (n=20): Length 13–26 μm, width 3.5–5 μm and striae density 36–40 in 10 μm. B. garrensis was found in 13 lakes and reached a high relative abundance (max=55.6%) in two western coastal peatland lakes which have been dammed for water abstraction. It was confirmed in three river samples in the west (max=9.6%) and had a low optima for pH relative to other taxa in the genus which may be important for environmental assessment ( Table 3).
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