This species forms dense continuous brown to greyish brown turfs under fucoids with localized tufts of Ceramium deslongchampsii Chauvin ex Duby growing through (Image A). Erect filaments are 35-50 µm wide and typically 0.5-1.5(2) cm tall and are sparsely bi(tri)furcately branched; the branches typically develop parallel to their bearing axis (Image B). Erect filaments have distinct apical cells that are rounded at the tip (Image C) and undergo transverse divisions to form large cells, which in turn undergo longitudinal divisions to form the multiseriate thallus segments. The axial elongate cells of these segments in turn can undergo subsequent transverse divisions to form irregularly divided axes (Image D), with undivided longitudinal cells (typically one per segment when well developed) converting to pericysts (Image E). The basal system consists of polystromatic crustose regions (Image F) and numerous horizontal stolons, which are augmented by descending rhizoids produced from lower cells of the erect axes (Image G). The descending rhizoids are typically free and do not form cortication around the erect axes. The only reproductive structures that we have observed are unilocular sporangia, which are borne on single celled latrals (Image H). Plastids are small and discoid and positioned around the cell periphery, pyrenoids are absent (Image I).
Forming mats under fucoids in the mid and lower intertidal zones, as well as in pools in the upper zone. We have few genetically verified records of this group with only two from Haida Gwaii and one each from ME, NB and NS. This entire order awaits a proper survey and taxonomic update in the Canadian flora.
Image A. Protohalopteris radicans forming a continuous brown turf under fucoids with localized tufts of Ceramium deslongchampsii Chauvin ex Duby growing through (mid intertidal on rock, Lepreau exposed biodiversity Site, NB; GWS032238).
Image B. Branching is sparse with branches typically resting parallel to their bearing axis (GWS032238).
Image C. Apical cells are large and rounded at the tip (mid intertidal on rock, Letete exposed biodiversity site, NB; GWS042850).
Image D. Secondary divisions of the longitudinal cells in the thallus segments are common but irregular resulting in tiers of 2-4 cells in each segment (GWS045857)
Image E. Pericyst (arrow) developing from an undivided cell in a thallus segment (GWS045857).
Image F. Polystromatic crustose region of the basal system (lower mid intertidal on rock, Lepreau exposed biodiversity site, NB; GWS045857).
Image G. Horizontal stolons and descending rhizoids contribute to the expansive basal system (GWS045857).
Image H. Unilocular sporangia borne on single celled laterals (lower mid intertidal on rock, Lepreau exposed biodiversity site, NB; GWS032393).
Image I. Numerous discoid plastids line the cell periphery (GWS042850).