Uniseriate filaments commonly contributing to green turfs on rock in the intertidal (Featured Image above) or more commonly mats in estuarine or salt marsh localities (Image A). Commonly associated with freshwater runoff (Image B). Filaments form tufted mats or tangled turfs (Image C). On closer view straight to rope-like strands (Image D), as well as strongly curled filaments (Image E) are typically mixed together in the mats. The uniseriate filaments are attached by a slightly modified basal cell (Image F). Filaments near the base are 7-8.5 µm wide, the cells squat to slightly rectangular, 6.5-8 µm wide by 6.5-12 µm tall (Images F & G). Similarly cells mid thallus can be variable, square to slightly disc like, 21-23 µm wide by 7-16 µm tall (Image H). Upper filaments 24-26 µm wide, the cells squat to slightly disc shaped, 21.5-24 µm wide by 7.2-11 µm tall (2-3:1 width to height ratio; Image I). Reproductive zoidangia (presumably gametangia) tend to be slightly squat, 21-24.5 µm wide by 14-17 µm tall (Image J). There may be akinete or aplanosporangia development in this species, but details were difficult to discern (Image K). In fresh material the chloroplasts form a band or ring that partially encircles the outer wall (covering 05.-0.7 of the cell periphery) with a single obvious pyrenoid in low (Images G & L) to mid (Image H) cells and 1-2 pyrenoids in upper (Image I) cells.
We have only five genetically verified collections of this species, although filaments that match this morphology were visible in most of our estuarine collections of other species. Those that are genetically confirmed range from Gwaii Hannas, BC, to Churchill, MB, and into estuaries of the Bay of Fundy, NB. They range from mid to high intertidal on cobble and rock (Featured image above), or contribute to tangled mats in estuaries (Image A) and salt marsh habitats. In many cases they are associated with freshwater outflows (Image B). Ulothrix implexa is most likely to be confused with Ulothrix flacca (Dillwyn) Thuret, but the latter is more typically marine in habit, has coarser filament walls owing to copious epiphytes and other adherent material, with the upper cells tending to be more strongly disc shaped.
It is common for what otherwise looks like a unialgal carpet on rock, or mat of green filaments in an estuary, to be a chaotic mix of green species including, among others, various Blidingia spp., Percursaria percursa (C.Agardh) Rosenvinge, Rhizoclonium spp., Rosenvingiella polyrhiza (Rosenvinge) P.C.Silva, Urospora spp. and Ulothrix spp. Identification should be done carefully, as should attempting to match DNA sequences to individual species. Owing to the wonders of PCR, a clean sequence could be from any one of the species present in a collection and not necessarily the dominant one on which the microscopical identification was based. Consequently, I am not yet 100% certain that the genetic groups and morphospecies (i.e. images below) completely align for the various Ulothrix spp. presented on this web site. Neither am I convinced that the correct binomial is applied to the morphospecies as outlined here. This is my best guess after consulting the pertinent literature (mostly Scagel (1966), Burrows (1991), Sears (2002), Brodie et al. (2007), Mathieson & Dawes (2017) and Gabrielson & Lindstrom (2018)). Notably, some accounts of Ulothrix implexa lack consistency between the written description and the images provided. Considerable work remains for this genus in our flora.
Image A. Specimen forming tangled mats on the upper mudflat at the head of the estuary (Oak Bay, NB; GWS045943).
Image B. Collection in freshwater outflow at the head of the estuary (upper intertidal on rock in freshwater outflow, at the head of the estuary, Oak Bay, NB; GWS045944).
Image C. Collections from high in an estuarine location in freshwater outflow (GWS045944).
Image D. Filaments can be straight and form rope-like strands (GWS045944).
Image E. Filaments can become curled and twisted (GWS045944).
Image F. Modified basal cell (arrow) forms the rhizoidal attachment (GWS045944).
Image G. Cells near the base range from squat to rectangular (GWS045944).
Image H. Cells mid thallus are typically squat to slightly disc shaped (GWS045943).
Image I. Cells in the upper filaments are typically squat to slightly disc shaped; some cells have two pyrenoids (arrows) (GWS045943).
Image J. Zoidangia formed in series (GWS045943).
Image K. Putative akinete or aplanosporangium (arrow) (GWS045943).
Image L. Filament (arrow) low thallus, each cell with a parietal ring like chloroplast with a single obvious pyrenoid. This species was found in a mix of greens including Rhizoclonium riparium (Roth) Harvey and, surprisingly, the supposedly rare Rosenvingiella polyrhiza (Rosenvinge) P.C.Silva (the more golden coloured filaments bottom and left; I missed that when processing the collections…) (high intertidal on mud wall near freshwater runoff, Mascarene Road estuary, Letete, NB; GWS044478, this collection awaits genetic verification).