Brachysira neglectissima Lange-Bertalot, 2004

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 : 13-14

Brachysira neglectissima Lange-Bertalot ( Figs 61–80 )

Valves are lanceolate with a continuum in outline observed from those that are clearly capitate, or gradually protracted, to those having distinctly narrow pointed ends ( Figs 71–80 ). Valve dimensions (n=53): Length 16–36.5 μm, width 4–5 μm and striae density 35–40 in 10 μm. Caution is required when applying the character of protracted ends to help with its separation from B. liliana (Hoffmann et al. 2013) ; a complete examination of the population is required. The greater width of B. liliana from the limited number of observations in our study was in agreement with guidance given in the same reference. A small number of frustules with a morphology comparable to B. neglectissima and co-occurring with it were more broadly elliptic in outline and possess an additional row of areolae (n=4 rows). Whether it represents a different taxon or merely further variation in B. neglectissima will require the study of more abundant populations ( Fig. 69 ). B. neglectissima occurred in 17 oligotrophic lakes and a single river station. It was widely distributed and found from the midlands to the Burren region and throughout the west and northwest. It reached maximum relative abundance (32.2%) in a high status calcareous lake (L. Bunny) but was also observed occasionally (1.3–3.4%) in low alkalinity lakes (4.0–8.0 mg/l CaCO 3) with near neutral pH (pH=6.8–7.1).

Brachysira brebissonii ssp. brebissonii Ross in Hartley, and Brachysira intermedia (Østrup) Lange-Bertalot ( Figs 81–98 )

The morphology of B. brebissonii ( Figs 81–91, 96–98 ) conforms to the recent analysis of what is considered to be the most likely type material for this species reported in Van de Vijver (2014). Non-protracted or almost non-protracted rhombic-valves, with acutely rounded apices dominate Irish populations. Although valves with more rounded ends were encountered occasionally, obtusely rounded valves were never observed. Valve dimensions (n=20): Length 14.5– 28.5 μm, width 5–8 μm and striae density 26–29(30) in 10 μm. B. brebissonii was found in 26 lakes and rivers draining siliceous peatland catchments on the periphery of the island and were absent from higher alkalinity regions in the Burren and midlands ( Fig. 2 ). Maximum abundance (12.4%) was recorded in L. Glendalough on the east coast with lower densities (0.2–4.9%) recorded for rivers systems along the Atlantic seaboard.

LM, separation of B. intermedia from B. brebissonii is via its more protracted outline ( Figs 92–95 ) relative to the obviously rounded obtuse ends in the latter species. Their similar morphology and a lack of SEM micrographs probably contributed to confusion with their identification during routine monitoring in the past. Another unidentified form, closely resembling B. intermedia in morphology was commonly encountered in Irish samples ( Figs 99–110 ). Its ultrastructure was dissimilar to B. intermedia , however differences in the structure of the striae, which always had 2 interstriae papillae and a greater relief between striae were distinctive ( Figs 106–109 ). Valve dimensions (n=20): Length 18–25 μm, width 5–6.5 μm and stria density 25.5–27.5 in 10 μm. This unknown valve form co-occurs with B. brebissonii . It was observed in samples from 13 lakes and 6 rivers and also reached a maximum relative abundance (12.8%) in L. Glendalough. It was combined with B. intermedia for calculating the environmental optima reported in this study. This morphotype may also to be illustrated in Hoffmann et al. (2013; Tafel 59, figs 19–20) and possibly in Wolfe & Kling (2001; fig. 13) and its formal relationship with B. intermedia requires further investigation.

Figures

FIGURE 2. The distribution of the more abundant Brachysira taxa in Irish lakes and rivers.

FIGURES 61–80. Brachysira neglectissima. Figs 61–70. LM. Figs 71–80. SEM. Scale bar = 10 μm for all LM figures. Scale bar in all SEM micrographs = 2 μm.

FIGURES 81–98. Brachysira brebisssonii and Brachysira intermedia. Figs 81–91. B. brebissonii, LM. Figs 92–94. B. intermedia, LM. Fig. 95. SEM, B. intermedia. Figs 96–98. SEM, B. brebissonii. Scale bar = 10 μm for all LM figures. Scale bar in all SEM micrographs = 2 μm.

FIGURES 99–110. Brachysira sp. (aff. B. intermedia). Figs 99–105. LM. Figs 106–110. SEM. Scale bar = 10 μm for all LM figures. Scale bar in all SEM micrographs = 2 μm.