Gaillona hookeri (Dillwyn) Athanasiadis (A)

This species forms brownish to purplish red tufts up to 4 (10) cm tall (Image A). Near the tips the axes are ecorticate and typically appear regularly alternately branched (Image B), the main axes with a weak sinusoidal pattern and rectangular cells 30-48 µm wide by 36-70 µm tall (Image C). However, careful observation below the tip reveals a branching pattern that transitions to spiral in habit (Image D), which can be observed mid thallus where the axial cells remain ecorticate and are 80-94 µm wide by 455-490 µm tall (Image E). Low on the axes branching can appear irregularly alternate to spiralled (Image F), the axial cells 80-90 µm wide by 124-140 µm tall (Image G) with a thin and loose covering of rhizoidal filaments (Image H). Tetrasporangia develop adaxially with lagging abaxial production on the upper filaments (Image I), these 50-56 µm wide by 58-69 µm tall, sessile and with tetrahedral division (Image J).

Initially I was uncertain about this identification as there are no matching COI-5P data in GenBank for our single record from NL. There is a COI-5P sequence attributed to this species in GenBank, but it is distant to the data for our specimen and is a 99.83 % match to a sequence for Aglaothamnion cordatum (Børgesen) Feldmann-Mazoyer. We recently acquired rbcL-3P data, which is only 1 bp divergent from a GenBank entry for Gaillona hookeri. As Chris Maggs was one of the authors on this latter sequence, I have more confidence that this name is correctly applied to our NL specimen.

Image A. Press of our only specimen from subtidal (12 m) on wood, English Harbour East Government Dock, NL (GWS007477; line is 2 cm).

Image B. Axis near the tip appearing regularly alternately branched (GWS007477; rehydrated from press).

Image C. Close up of main axis and branching pattern near the tip (GWS007477; rehydrated from press).

Image D. Branching has a spiral pattern (arrows) moving from the tip (GWS007477; rehydrated from press).

Image E. Branching has a spiral pattern (arrows) lower mid thallus (GWS007477; rehydrated from press).

Image F. Lower axes are relatively robust with irregularly alternate to spiral branching (GWS007477; rehydrated from press).

Image G. Close up view of lower axial vegetative cells (GWS007477; rehydrated from press).

Image H. Close up of rhizoidal cortication around the main axis (GWS007477; rehydrated from press).

Image I. Adaxial tetrasporangial production proceeds abaxial development on upper filaments (GWS007477; rehydrated from press).

Image J. Tetrasporangia sessile and with a tetrahedral division pattern (GWS007477; rehydrated from press).