Brachysira garrensis (Lange-Bertalot & Krammer) Lange-Bertalot, 1994

Kennedy, Bryan & Allott, Norman, 2017, A review of the genus Brachysira in Ireland with the description of Brachysira praegeri and Brachysira conamarae, new raphid diatoms (Bacillariophyceae) from high status waterbodies, Phytotaxa 326 (1), pp. 1-27 : 16

Brachysira garrensis (Lange-Bertalot & Krammer) Lange-Bertalot ( Figs 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 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 & Figs 160–165 ) and smaller capitate valves of B. microcephala with dense striae ( Figs 129 , 244–246 ). 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).

Figures

FIGURES 111–135. Brachysira garrensis. Figs 111–130 LM. Fig. 135–SEM. Scale bar = 10 μm for all LM figures. Scale bar in all SEM micrographs = 2 μm.

FIGURES 136–172. Brachysira microcephala morphotype BMIC-1. Figs 136–165. LM. Figs 166–172. SEM. Scale bar = 10 μm for all LM figures. Scale bar in all SEM micrographs = 2 μm.

FIGURES 240–252. Brachysira microcephala morphotype BMIC-4. Figs 240–246. LM. Figs 247–252. SEM. Scale bar = 10 μm for all LM figures. Scale bar in all SEM micrographs = 2 μm.