Our single collection is ~16 cm tall, sparsely branched to 3-4 orders with the final order branches short and at 90o angles to their bearing axes (Image A). Sections were difficult to obtain from rehydrated material, but both transverse (Image B) and long (Image C) sections reveal large loosely compacted filaments of rectangular medullary cells, 35-80 µm wide by 60-145 µm tall, becoming progressively smaller, 11-13 µm wide, toward the surface and augmented by more darkly staining rhizoidal filaments, and finally an outer covering of assimilatory filaments. Although assimilatory filaments are found on the larger medullary cells directly (Image D), they are more typically on the outermost layer of narrow more heavily staining cells (Image E). Assimilatory filaments range from 4 to 14 cells in length, are typically only branched low on the filament, and are curved and clavate (Image F). Their lower cells are rectangular oval, 9-11 µm wide by 14-22 µm long, while terminal cells are 16-18 µm wide by 21-24 µm long (Image F). Although largely lost in processing, multicellular bases were abundant indicating that hairs are common (Image E). Unilocular sporangia are oval, 34-38 µm wide by 40-45 µm wide, and are produced either low on the assimilatory filaments, or at times may replace them (Image G).
We have a single collection from the subtidal on rock, Bottle Cove, NL. It was originally identified as Cladosiphon zosterae (J.Agardh) Kylin, but our data failed to match other sequences in GenBank assigned to this species (not that this is necessarily a concern in its own right). Further investigation indicates that this species is superficially similar to Cladosiphon zosterae (J.Agardh) Kylin, but differs in subtle aspects of the transition from medulla to the assimilatory filaments. Harvey (1851, page 127, plate 10A; as Mesogloia zosterae Areschoug) appeared to have our species in his studies assigning it with some hesitation to Cladosiphon zosterae (J.Agardh) Kylin. Farlow (1881; p. 86; as Castagnea zosterae (J.Agardh) Thuret) noted that the plant depicted in Harvey was different from bona fide Cladosiphon zosterae (J.Agardh) Kylin in that Harvey reported the assimilatory filaments arising from narrow pigmented outer filaments rather than directly on the large outer cortical cells. As noted above, both can occur in the current specimen. Taxonomic work is needed, as well as bona fide collections Cladosiphon zosterae (J.Agardh) Kylin from our flora. The assignment of this species to Polycerea is tentative pending further study (see Polycerea borealis Vinogradova for discussion).
Image A. Press of our only specimen from the subtidal, Bottle Cove, NL (GWS007380).
Image B. Transverse section displaying loosely compacted large central filament cells and outer assimilatory filaments on narrow outer strongly staining cells (GWS007380; rehydrated, aniline blue).
Image C. Long section displaying large central medullary cells and outer assimilatory filaments and unilocular sporangia typically on narrow outer cells (GWS007380; rehydrated, aniline blue).
Image D. Assimilatory filaments borne on relatively clear broad medullary cells (GWS007380; rehydrated, aniline blue).
Image E. Assimilatory filaments borne on outer moderately stained narrow cells. Multicellular base of a pheaophycean hair (arrow) evident (GWS007380; rehydrated, aniline blue).
Image F. Assimilatory filaments are 4-14 cells long, curved and clavate (GWS007380; rehydrated, aniline blue).
Image G. Unilocular sporangia on short stalks or borne laterally low on assimilatory filaments (GWS007380; rehydrated, aniline blue).