This species starts out as a slightly gooey, light green sac that then splits open into a green blade, which is 3-10 cm tall (Image A). In surface view mid thallus the cells are irregular in shape, typically angular, 7-18 µm in dimensions, separated by relatively thick walls, and tend to be clustered in groups of 2-4 (Image B). Lower on the thallus cells can be larger, 11-29 µm, and less regular in distribution, but still maintain spaces between them (Image C). Cells near the base produce descending anchoring rhizoids (Image D). Each cell contains a single parietal chloroplast that occupies most of the cell surface and contains 1(2-3) pyrenoids (Images B-D). In cross section blades are monostromatic, only 17-24 µm wide, the cells isodiametric with rounded corners and the plastid confined to the outer (original tube) wall (Image E). The margins tend to be irregular and wavy, at times locally dentate in appearance (Image F).
We have few records for this species (BC n = 1; NW Atlantic n = 8), which is a sampling artifact. Predominantly collected in the late fall to early spring, and typically in estuarine and salt marsh environments rather than on open coast, it has unquestionably missed our attention. Locally abundant is the best term, and typically where freshwater flows over cobble into an estuary in our experience (see Featured Image above). This species is also reportedly collected in our Arctic flora, but we have not encountered it to date. Easily confused with Monostroma spp. (e.g. Monostroma grevillei (Thuret) Withering), species of that genus have the cells more tightly clustered in surface view and are more typically encountered at sheltered to exposed sites.
Sequences for rbcL (HQ603384), tufA (HQ610252) and UPA (HQ603329) are correctly associated with this species and were incorrectly assigned to Kornmannia leptoderma (Kjellman) Bliding in Saunders & Kucera (2010).
Image A. Specimens growing in early December in full freshwater outflow at the head of the Mascarene Road estuary, Letete, NB (GWS044445).
Image B. Surface view of vegetative cells mid thallus, associated in groups of 2-4 and separated by thick walls (GWS044445).
Image C. Surface view of vegetative cells low on the thallus, still separated by thick walls, but less patterned in distribution (GWS044445).
Image D. Surface view of rhizoidal development from cells closest to the thallus base (GWS0444455).
Image E. Section of the monostromatic thallus, the chloroplasts typically with a single pyrenoid concentrated on one surface (GWS044445).
Image F. View of the irregular, dentate margin (uppermost intertidal on cobble in freshwater outflow, Mascarene Road estuary, Letete, NB; GWS037942; rehydrated from press).