Cladophora pygmaea Reinke (A)

Individuals are tiny, typically 2-3 mm tall, and dark green with an overall secund appearance at the macro level (Image A). At low magnification the branched filaments, as well as descending rhizoids, are clearly evident (Image B). Although thalli are anchored by a basal cell that appears similar to other vegetative cells, the anchoring is augmented by these descending rhizoids (Image C). Mid thallus cells are irregular in shape and size (Image D) with rhizoids developing from the base of some cells, especially where branching occurs (Image E). Branching is terminal to quasi lateral (Image F) and lenticular cells (branch and or rhizoid initials?) are common (Image G). Apical cells are round at the tip (Image H). Cellular walls are laminate in appearance (Image I) while the chloroplasts are parietal and reticulate and contain multiple pyrenoids (Image J).

I had pretty much come to the conclusion that this species is not in our NW Atlantic flora, however, a visit to Sam Orr’s Pond once again turned up the unusual (for other examples see Saunders et al. (2013) and Savoie & Saunders (2019)). Nonetheless, the Cladophora pygmaea Reinke was only discovered back in the lab as I teased apart a collection of an attached but yet to be identified Chaetomorpha (Image K). However, ITS sequences generated for our two Sam Orr collections are a 99.6 % match to data in GenBank for a specimen from NC identified as Cladophora albida (Nees) Kützing (KX281887). More study is needed.

Image A. Individual being prepared for microscopy after a surprise discovery among filaments of a larger Chaetomorpha sp. (upper pond submerged on rock, Sam Orr’s Pond, NB; GWS044467).

Image B. Gross morphology of an individual including weakly secund branching and descending rhizoids (upper pond submerged on rock, Sam Orr’s Pond, NB; GWS044450).

Image C. Basal cell of a filament and descending rhizoids (GWS044467).

Image D. Cells were irregular in size and shape (GWS044467).

Image E. Rhizoid from the base of a cell at a point of branching (GWS044467).

Image F. Branching was terminal to quasi lateral on the bearing cell (GWS044450).

Image G. Lenticular cells were common (GWS044450).

Image H. Apical cells are rounded at the tip (GWS044467).

Image I. Cell walls are obviously laminate (GWS044467).

Image J. View of the parietal reticulate chloroplast with multiple pyrenoids (GWS044467).

Image K. Unidentified Chaetomorpha sp. which overgrew the much smaller individuals of Cladophora pygmaea Reinke (upper pond (near tidal rapids) submerged on rock, Sam Orr’s Pond, NB; GWS044466).