This species forms a dull green film in the uppermost intertidal and is easily dismissed. Our single collection consists of tangled filaments, which when spread in our collecting tray (Image A) suggested perhaps a species of Urospora (e.g. Urospora neglecta (Kornmann) Lokhorst & Trask). Molecular data indicated an alliance to Prasiola stipitata Suhr ex Jess and prompted a look at the voucher. In whole mount the prostrate filaments are uniseriate and narrow, 15-20 µm wide, with domed apical cells and vegetative cells that are disc shaped being 3X wide as tall (Image B). Where the prostrate filaments contact the substratum they can produce unicellular anchoring rhizoidal filaments singly or in series (Image C). Erect filaments start out very much as described for the prostrate filaments, but eventually have mixed regions of uniseriate and multiseriate growth (Image D) the latter becoming extensive in longer axes the result being unbranched, solid terete axes up to 75 µm in width (Image E) and 2-3 cm tall. In fresh material each cell reportedly has a lobed to stellate chloroplast with a single pyrenoid.
We have a single collection of this species from upper intertidal on rock at Duck Islands, Torngat, Labrador, NL. It was taken while aboard the MV Race on a biodiversity blitz expedition from Qikiqtarjuaq, NU, to Saint Pierre and Miquelon, France (just south of NL) in 2014 (Image F). This reportedly rare species (our limited observations concur) co-occupies that uppermost intertidal fringe in the NW Atlantic with Prasiola stipitata Suhr ex Jess. We have also reason to believe that it grows tangled among the thick green mats associated with estuarine locations in the Bay of Fundy (see image L for Ulotrhix implexa (Kützing) Kützing). Present well into the fall in the north becoming progressively a late winter spring annual to the south. This species is easily distinguished from its congener Rosenvingiella radicans (Kützing) Rindi, McIvor & Guiry.
Image A. An image of our only collection from the upper intertidal on rock, Duck Islands, Torngat, Labrador, NL (GWS039307).
Image B. Uniseriate prostrate filament with disc shaped cells and domed apical cell (GWS039307; rehydrated from press).
Image C. Uniseriate prostrate filament producing a series of unbranched anchoring rhizoids (GWS039307; rehydrated from press).
Image D. Erect axes uniseriate with localized multiseriate parenchymatous regions (GWS039307; rehydrated from press).
Image E. Fully parenchymatous erect axes develop in the longest filaments (GWS039307; rehydrated from press).
Image F. Our first view of the MV Race prior to a three-week Arctic biodiversity blitz expedition from Qikiqtarjuaq, NU, to Saint Pierre and Miquelon, France (just south of NL) in 2014. One heck of a trip.