Pseudostaurosira brevistriata

This taxon is considered to be widespread in freshwater, being reported from across the US and elsewhere (Patrick and Reimer 1966, Lawson and Rushforth 1975, Clark and Rushforth 1977, Foged 1977, Foged 1981, Kaczmarska and Rushforth 1983, Cox 1996, Camburn and Charles 2000, Siver et al. 2005, Bahls 2021). However, after examining the type material, Morales et al. (2015) suggested that it may be less widely distributed has been believed. Verified reports are from Alaska (Foged 1981), the northeastern US (Camburn and Charles 2000), the Great Lakes (Reavie and Kireta 2015), the western US, (Bahls 2021). Although widely distributed and commonly encountered, this taxon is rarely reported in great abundance (Lawson and Rushforth 1975, Clark and Rushforth 1977, Kaczmarska and Rushforth 1983, Antoniades et al. 2008). Bahls (2021) reports occurrences from lakes, ponds, rivers, and streams.

In the Great Lakes National Parks (Edlund et al. 2011, 2012, 2013), it is common (>5% relative abundance) in shallower lake sediment cores from lakes in Voyageurs (Ryan, Locator, and Elk lakes), Isle Royale (Harvey and Ahmik lakes), Pictured Rocks (Beaver Lake), and Sleeping Bear Dunes (Manitou, Bass, and Shell lakes).

This taxon is commonly reported to prefer alkaline waters and be relatively indifferent to nutrient content. Foged (1981) stated, “Oligohalobe (indifferent). Alkaliphile.” regarding the five populations he observed from Alaska. Cox (1996) reported that it occurs in, “oligotrophic to eutrophic waters”. Siver et al. (2005) reported it from six mesotrophic ponds in Cape Cod. Bahls (2021) reported that the populations observed from the western US preferred cool, alkaline waters with moderate nutrient content and conductivity.

Many research groups consider it as an indicator organism and published regional environmental optima and tolerances including:

Wilson et al. (1994): Salinity optimum - 0.25 g/L with a lower limit of 0.04 g/L and an upper limit of 1.40 g/L for populations from lakes on the interior plateau of British Columbia, based on a broad morphological species concept.

Camburn and Charles (2000): Abundance Weighted Mean (AWM) pH – 7.30, pH Tol – 0.65, AWM ANC – 217µeq/L, ANC Tol – 132 µeq/L, AWM Total Al – 38 µg/L, Total Al Tol – 68 µg/L, AWM DOC – 102 µmol/L, DOC Tol – 183 µmol/L, AWM TP – 13.73 µg/L, TP Tol – 6.02 µg/L from low alkalinity lakes in the northeastern US. It is worth noting that at the time of this publication a very broad morphological concept was being applied to this taxon (amongst many others), and the authors present specimens under this identity which we would now recognize as entirely different genera (Plate 6, fig. 8). The specimen which most closely resembles the type population examined by Morales et al. (2015) was identified as “Fragilaria brevistriata var. capitata” (Plate 6, fig. 15).

Reavie and Smol (2001): TP - 0.017 mg/L, pH – 8.02, TN – 0.470 mg/L, Max Depth – 17.2m, Chla – 1.66mg/L. At the time of this publication a broad morphological species concept was being applied to this taxon.

Siver et al. (2005): pH optima – 7.2 +/- 0.3, TP optima – 13.6 +/- 4.0 µg/L from ponds in Cape Cod. Some of the larger specimens may be an acceptable fit for P. brevistriata however the smallest specimens appear to belong to a different taxon, potentially P. microstriata.

Reavie and Kireta (2015): TP optima >30 µg/L, Cl optima between 10 and 50 µg/L. This taxon is reported to be a weak indicator of stress. Although some specimens identified by these authors conform well to type material, the specimens with linear valve outlines and apices which are more rounded than rostrate may represent other taxonomic entities (see Plate 23, fig. 9), the specimens identified as P. brevistriata var. inflata appear to be a better fit for the type population presented by Morales et al. (2015). Similar environmental optima are reported from both the nominate variety as var. inflata.

Bahls (2021): AWM Conductivity – 552 µS/cm, AWM pH – 7.6, AWM Temperature – 15.3 °C, AWM TN – 430 µg/L, AWM TP – 47 µg/L from rivers, streams, lakes and ponds in western US. Bahls appears to have based his treatment of this taxon on the morphological species concept proposed by Morales et al. (2015), and as such, presented specimens which closely conform to that morphological species concept, albeit with the exception of some specimens with strongly produced apices. The authors of this page consider this to be an acceptable level of variability.