Tufts of soft tubular thalli 1-10 cm tall, yellowish brown to green in color (Image A). Cells near the plant base become rhizoidal in some individuals forming the attachment to the substratum (Image B), but typically these cells are only weakly modified (Image C). Even at low magnification this species stands out among other green algae as the cells are in obvious groups of (two or) four, these in turn in distinct longitudinal rows (Image D). Lower regions of the thalli are 40-80 µm wide with cells 3-6 µm in diam. (Image E). Distally thalli can become 1-2 mm wide, but the cells (5-11 µm in diam.) are still in groups of four and arranged in longitudinal rows (Image F). In younger individuals tips can be uniseriate (Image G). Chloroplasts are typically cup-shaped with a single pyrenoid (Image H).
We have a handful of collections from the Bay of Fundy, these submerged on rock in a shallow salt marsh pond or on rock or cobble on (semi-)sheltered coasts in areas of freshwater seepage and runoff. This species has been listed for BC (Gabrielson & Lindstrom 2018) while its presence in the Arctic remains unverified through genetic tools. More genetically verified collections are needed to determine the full geographical range of this species. Also see comments under Pseudothrix groenlandica (J.Agardh) Hanic & S.C.Lindstrom.
Image A. Thalli taken from low intertidal cobble in freshwater runoff at Mispec Beach, NB (GWS045294).
Image B. Elongate cells near the base of a tube (subtidal on rock, in tidal marsh pond, Sam Orr’s Pond; GWS010966; rehydrated from press).
Image C. Cells near the base that are only slightly modified (upper intertidal on rock with freshwater seepage, Duck Pond Beach, NB; GWSX047097).
Image D. Low magnification reveals the highly ordered rows of cells arranged in groups of four (upper intertidal on rock with freshwater seepage, Duck Pond Beach, NB; GWSX047062A).
Image E. Low on the tube cells are organized in clusters of four that are arranged in longitudinal, and to a lesser extent transverse, rows (GWS010966; rehydrated from press).
Image F. Near the top of the tube cells divide to form clusters of four cells (GWS045294).
Image G. Uniseriate tip of a younger thallus (GWS045294).
Image H. Chloroplasts are cup-shaped and contain a single large pyrenoid (arrows) (GWS045294).