Erythrotrichia carnea (Dillwyn) J.Agardh (BC/A)

This microscopic species can be difficult to find in the field, but can be so abundant that it can discolour other filamentous algae on which it grows (Image A). The typically (pseudobranching may occur) unbranched filaments can reach 6-8 cm in length with the cells squat to rectangular in shape, 13-17 µm wide by 16-28 µm long (Image B). Each cell contains a stellate chloroplast with an obvious central pyrenoid (Image B). The basal cell is lobed and attaches the filament to the substratum (Image C).

This species reportedly grows on shell, stone or epiphytic on other algae in quiet waters from the mid intertidal to subtidal (15 m). Our few collections of this commonly overlooked species were on and tangled with other algal species. We have yet to assess if this morphospecies corresponds to a single genetic group in BC and the NW Atlantic. Work is ongoing. There is a slight chance of confusion with Stylonema alsidii (Zanardini) K.M.Drew, but that species is smaller with smaller vegetative cells, is typically branched, and has an unmodified basal cell.

Image A. Filaments of Erythrotrichia carnea growing among those of other red algae (drift on Ceramium sp. 1G0SL, Beach to east of Parlee Park Beach, NB; EGWS001131).

Image B. Close up of cells revealing stellate chloroplasts each with a central pyrenoid (EGWS001131).

Image C. Close up of a lobed basal cell (arrow) (EGWS001131; fixed in formaldehyde, stained with aniline blue).