Protomonostroma undulatum (Wittrock) K.L.Vinogradova (BC/Ar?/A)

This species forms delicate light green blades with highly ruffled margins, typically 2-6 cm wide and up to 24 cm tall (Image A). Vegetative cells mid thallus in surface view are angular in outline and are 12-25 µm in dimensions (Image B). In cross section the blade is clearly monostromatic and 24-30 µm wide (Image C). Near the base the cells become rhizoidal in habit and, in this fixed material, the single prominent pyrenoid per cell is visible (Image D).

We have only 12 genetically verified records of this species. They extend from mid intertidal pools to the subtidal (3 m), and are commonly growing on other algae, or at times on rock or other hard substrata. Our records extend from RI to the lower Bay of Fundy, NB, but this species reportedly extends much farther north and is reported in BC. We have a genetic record from Kamchatka, which is consistent with the reportedly wider distribution. A late winter spring annual.

Image A. Specimen growing on Mastocarpus stellatus (Stackhouse) Guiry in the low intertidal at Harrington Cove, Grand Manan, NB (GWS003761).

Image B. Vegetative cells in surface view mid thallus (low intertidal on Corallina officinalis Linnaeus, Starboard, ME; GWS003666; rehydrated from press).

Image C. Vegetative cells in cross section mid thallus (GWS003666; rehydrated from press).

Image D. Vegetative cells in surface view near the base becoming rhizoidal in habit. Pyrenoids (arrows) remain visible in this fixed material (low intertidal on Mastocarpus stellatus (Stackhouse) Guiry, Harrington Cove, Grand Manan, NB; GWS002157; rehydrated from press, but fixed in formaldehyde prior to pressing).