Valves are lanceolate, becoming rhombic in smaller specimens, ends cuneate and slightly protracted in larger specimens. The valve face is flat and largely hyaline. Short striae are composed of a single large areola (rarely 2), restricted to the valve margin.
A short spathulate spine is present on the margin, interrupting each stria. Stria density varies from 12 to 22 in 10 µm. A small porefield is present on both apices and is visible with SEM, appearing sunken in internal view.
In the original description (Marciniak 1982), it is noted that some specimens are up to 20 µm in length and these should be described as a new species. We also documented such larger specimens (see Autecology images). Plots of valve dimensions of our populations (from Harvey Lake, Isle Royale National Park, SMM 13293) do not indicate a clear species boundary.
Marciniak (1982) also notes that this taxon occurs with Fragilaria brevistriata Grunow. She also notes that these two taxa are similar in size and shape, but that P. microstriata possesses a more subtle ornamentation. Still, these taxa may be difficult to distinguish.
In 2016, Spaulding and Bishop initiated correspondence with Dr. Elwira Sienkiewicz, of the Polish Academy of Sciences, in attempts to locate the type material. We understand that the Marciniak collection, including the type materials for P. microstriata, are currently inaccessible, located in an unspecified warehouse outside of Warsaw. Dr. Sienkiewicz, however, did note that she is in possession of materials from the type location of the taxon.
This taxon has been reported from the Laurentian Great Lakes, with the greatest relative abundance in Lakes Michigan and Huron, and widely distributed in coastal wetlands (Reavie and Kireta 2015). Morphometrics were reported as length (5.5-9.5 µm), width (1.5-3.3 µm), striae (17-22 in 10 µm). These sites had total phosphorus concentrations of 30 µg/L and chloride of 10 µg/L. Other forms, similar to Pseudostaurosira microstriata, were reported as P. microstriata var. 1 UMD, P. microstriata var. 2 UMD, and P. microstriata/elliptica UMD.
It was also reported (as Fragilaria cf. microstriata FMST; length 6-9 µm, width 2-3 µm, striae 18-24 in 10 µm) from rivers in Quebec (Lavoie et al. 2008). Others report it as rare (as Fragilaria brevistriata var. #1 SLR) from sediment cores of the St. Lawrence River (Reavie and Smol 1998).
In the Great Lakes National Parks network, this taxon is found from low to medium relative abundance in sediment cores from shallow lakes in Voyageurs National Park (Ek and Ryan lakes), Isle Royale National Park (Harvey Lake), and Apostle Islands National Lakeshore (Outer Lagoon).
Fragilaria microstriata nov. sp. (Pl. II, Figs 5,6)
Frustulum faci laterali visum - rectangularu. Valvae tenues, media parte extensae, lanceolae et rhombi forma, apicibus paulo aut magis prolongatis, capitulatis aut obtuse rotundatis. Valvae 5.5 - 7.5 µm (20 µm) longae, 2.1 - 3.3 µm latae. Striae transversae breves, in margine valvae 9-11 in 5 µm. Area oblonga, lata, lanceolata. Inveniebantur nonnullae valvae prolongatae ad 20 µm quae distinguendae sunt et describendadae ut nova varietas speciei.
Frustule rectangular in girdle view, valves small and widened at the middle, lanceolate or rhomboidal with slightly or more strongly elongated ends, obtusely or capitately rounded apices. Valves 5.5 - 7.5 µm (20 µm) long, 2.1 - 3.3 µm wide. Transversal striae short, 9 - 11 in 5 µm. Longitudinal area wide, lanceolate. Sometimes the valves are very elongated (up to 20 µm/long) that should be distinguished and described as a new variety of the species.
Type locality: sediments of the Przedni Staw Lake, Tatra Mts., Poland.
Type slide: no. 3024 in coll. of Institute of Geological Sciences, Polish Academy of Sciences, Warsaw (B. Marciniak).
Fragilaria microstriata nov. sp. is common in the sediments of the Przedni Staw Lake, it occurs together with Fragilaria brevistriata Grun., but it possesses a more subtle ornamentation.
Edlund, M., Bishop, I., Allen, L., Spaulding, S., Mohan, J. (2023). Pseudostaurosira microstriata. In Diatoms of North America. Retrieved April 26, 2024, from https://diatoms.org/species/pseudostaurosira-microstriata
The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Pseudostaurosira microstriata from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:
ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.
