This species appears more like green filaments than tubes (Image A) owing to the narrow nature of the thallus being at its widest ~450 µm (Image B). Commonly forming tangled mats of individual tubes ~1-2 cm long. Short proliferations and spines are distributed across the entire thallus in some individual tubes (Image B), whereas only slight protuberances occur in others (Image C). Actual branching is rare, but does occur (Image D). Multiple tubes arise from the parenchymatous basal cushion (Image E) with cells near the base and into the cushion elongate (Image F) to weakly rhizoidal (Image G). In surface view low (Image H) and mid (image I) tube, cells are arranged in regular rows, being squat to elongate 4-9 µm wide by 4-10 µm tall. Near the top of the tube the cells are more irregular in shape, but of similar dimensions, occurring in rows in narrow tubes (ImageJ), but the rows tend to meander in wider tubes (Image K). In section the tubes are only 9-12 µm wide and lack a thick inner wall (Image L), which is also apparent in optical section (adjusting the focal plane; Image M). In fresh material plastids are stellate and lobed with an obvious central pyrenoid (Images N & O).
Our few collections are from upper intertidal on rock at exposed sites, growing on Fucus at a sheltered site, or growing on and tangled among salt marsh vegetation in estuaries including in direct freshwater outflow. We have a single collection from northern BC, and four from the Bay of Fundy, NB, but this species is likely much more widely distributed in Canadian waters (likely overlooked as just another Urospora looking thing). This genetic groups has a number of matches for a variety of markers in GenBank including sequences assigned to Blidingia minima (Nägeli ex Kützing) Kylin from China, as well as assigned to Blidingia marginata from Germany and Japan. Whether this entity or its sister “Blidingia marginata (J.Agardh) P.J.L.Dangeard ex Bliding Species2” is the true match to the morphospecies Blidingia marginata (J.Agardh) P.J.L.Dangeard requires further taxonomic study.
Image A. Specimens in the uppermost intertidal tangled among salt marsh plants and drift fucoids, St. Andrews (Blockhouse), Bay of Fundy, NB (GWS030298).
Image B. Tubes are narrow and can bear short proliferations and spines (mid upper intertidal on Fucus, Butze Rapids, Prince Rupert, BC; GWS004837; rehydrated from press).
Image C. At times the marginal proliferations are simply small bumps of a few cells (uppermost intertidal on rock, Letete exposed biodiversity site, Bay of Fundy, NB: GWS003689; rehydrated from press).
Image D. Branching is rare (uppermost intertidal in dried creek on cobble, Estuary along Lorenville Rd, NB; GWS044475).
Image E. Multiple tubes arise from parenchymatous cushions (GWS044475).
Image F. Cells at the tube cushion interface are elongate (arrow), but not strongly rhizoidal (GWS003689; rehydrated from press).
Image G. Elongate cells near the base, some weakly rhizoidal (uppermost intertidal on marsh grasses, uppermost estuary at culvert of Oak Bay, NB; GWS045946).
Image H. Cells near the base of a tube occur in rows (GWS044475).
Image I. Cells near mid thallus occur in rows (GWS004837; rehydrated from press).
Image J. Cells near the thallus top occur in loose rows in a narrower tube (upper intertidal tangled in salt marsh vegetation in freshwater outflow, Cottonii’ Creek, near Letete, NB; GWS036909; rehydrated from press).
Image K. Cells near the thallus top in wider tubes occur in weak meandering rows (GWS003689; rehydrated from press).
Image L. Section of a narrow tube (GWS036909; rehydrated from press).
Image M. Absence of a thickened inner wall can be observed in optical section (GWS004837; rehydrated from press).
Image N. Chloroplasts are stellate and lobed with an obvious central pyrenoid (GWS044475).
Image O. Chloroplasts, stellate and lobed with an obvious central pyrenoid, at higher magnification (GWS045946).