Specimens are 2-14 cm tall, yellow-brownish to dark red, and can appear subdichotomous (Image A) to more alternately branched (Image B), the latter associated with a greater abundance of well-developed adventitious branches. Individuals are attached by descending rhizoids at the base (Image C). The tips are forcipate and strongly inrolled (less so on tetrasporophytes) forming a distinctive feature for many species in this genus (Image D) and apical cells are rounded (Image E). Primary branches occur every 8-20 segments and adventitious branches can be infrequent to abundant (Image F). This species is fully corticated (Images D-F), although in some individuals the emergence of some of the larger underlying cortical cells can be viewed in whole mount (Image G). Near the tips the segments range from 0.8-0.9 diameters long, approaching ~1.2-1.6 diameters long mid to lower thallus where the complete cortication remains obvious (Image H). Gland cells are absent, but hyaline hair mother cells and their hairs (Image I) range from rare to abundant on different specimens. Cross section at the nodes reveals 6(7) periaxial cells (Image j). Carposporophytes are barely visible to the unaided eye, 265-396 µm wide by 222-326 µm tall, squat to rounded, and consist of 1 dominant gonimolobe and 1-2 suppressed gonimolobes (sequential development) and either lack (Image K) or produce only 1(2) involucral branches (Image L). Tetrasporangial production occurs in a single tier at the nodes and typically only 1-2(3) are visible at each node (Image M). Tetrasporangia are variously tetrahedral (Image N) to cruciate (Image O) or decussate (Image P) and are round to oval, 45-60 µm wide by 53-74 µm tall. They are either slightly emergent at the surface of the thallus (Image P) or retain a thin cortical cover (Image Q).
We have 17 genetically verified records, one from the subtidal (2 m) on Grateloupia turuturu Yamada in RI, the remainder from the Northumberland Strait, NB, typically subtidal (1 m) seagrass. Confusion with Ceramium virgatum Roth is possible with only vegetative material in hand. Reproductively Ceramium sp. 2virgatum has fewer involucral branches associated with its carposporophytes, and only 1-2(3) tetrasporangia are evident at a node, and these generally in a single tier. In addition, south of Cape Cod confusion with Ceramium secundatum Lyngbye is also possible, but similar reproductive differences apply, as well as 7-9 periaxial cells being evident when viewed in cross section.
The rbcL-3P for Ceramium sp. 2virgatum is 4 bp divergent from data in GenBank for Ceramium derbesii Solier ex Kützing, while data for COI-5P are a distant sister to Ceramium secundatum Lyngbye. The previous suggest that Ceramium sp. 2virgatum is a distinct species. This species may correspond to Ceramium circinatum (Kützing) J.Agardh in Taylor (1962), but the type locality for this species is Corsica and rbcL data currently in GenBank for this species are strongly divergent from those generated by us for Ceramium sp. 2virgatum. Further, Taylor (1962) and subsequently Schneider et al. (1979) called into question the presence of Ceramium circinatum (Kützing) J.Agardh in our flora. Ceramium sp. 2virgatum is either a new species endemic to our flora, or something introduced from elsewhere for which data have yet to be added to GenBank. Taxonomic work is necessary.
Image A. Pressed voucher characterized by subdichotomous branching (drift on seagrass, Kouchibouguac lagoon seagrass beds, NB; GWS006223).
Image B. Pressed voucher with a more alternately branched appearance (low intertidal on sandstone, St. Thomas, Northumberland Strait, NB; GWS007991).
Image C. Attachment pad formed of descending rhizoidal filaments (subtidal (1 m) on seagrass, Tabusintac, NB; GWS027655; rehydrated from press).
Image D. Tips are typically strongly enrolled (GWS006223; rehydrated from press).
Image E. Apical cells are rounded (GWS027655; rehydrated from press).
Image F. Primary branches are produced every 8-20 segments, while adventitious branches (arrows) range from infrequent to abundant (GWS006223; rehydrated from press).
Image G. Axes are fully corticated although occasionally at nodes underlying larger cortical cells (arrows) are exposed (GWS027655; rehydrated from press).
Image H. Fully corticated axis lower mid thallus, segments ~1.6 diameters long (GWS006223; rehydrated from press).
Image I. Hair cell (arrow) and subtending mother cell (GWS007991; rehydrated from press, aniline blue stained).
Image J. Section mid thallus revealing central axial filament and six periaxial cells (subtidal (1 m) on seagrass, Hay Island, NB; GWS027617; rehydrated from press, aniline blue stained).
Image K. Carposporophyte with an immature (arrow) and mature gonimolobes in the plane of focus, lacking involucral branches (low intertidal on rock, Cap des Caissie, North of Shediac, NB; GWS007975; rehydrated from press).
Image L. Carposporophyte with a single involucral branch (GWS007975; rehydrated from press).
Image M. Tetrasporaniga develop in a single tier at the nodes (subtidal (1 m) on seagrass, Hay Island, NB; GWS027619; rehydrated from press).
Image N. Tetrahedral tetrasporangium viewed in section (GWS027617; rehydrated from press, aniline blue stained).
Image O. Cruciate tetrasporangium viewed in section(GWS027617; rehydrated from press, aniline blue stained).
Image P. Decussate tetrasporangium, which is slightly emergent at the thallus surface (GWS027617; rehydrated from press).
Image Q. Irregularly tetrahedral tetrasporangium with a thin veil of surface cortication (GWS027619; rehydrated from press).