Pseudothrix groenlandica (J.Agardh) Hanic & S.C.Lindstrom (Ar/A)

Gametophytes are unbranched dark dull green tubes growing in tufts to 10 cm tall (Image A). Individual tubes are anchored by descending unicellular rhizoids formed at the base of the tube (Image B). Above the rhizoidal development the tubes are thin (30-80 µm wide), threadlike and reportedly solid. Here the cells develop in obvious clusters of 2-4, being angular, 5-10 µm diam., and separated by a visible line in the surface (Image C). Mid thallus and toward the tips, where blades reach 1-2 mm in width, cells are again angular but more irregularly distributed, 5-13 in diam., and well spaced not being tightly compacted (Image D). Cross section reveals a tube that is 46-54 µm thick, the cells being palisade in appearance, 6-10 µm wide by 22-30 µm long (Image E).

Again we have but one collection of this species, on rock from a low intertidal pool at Harrington Cove exposed biodiversity site, Grand Manan, NB. I am not even sure that this identification is correct and was surprised at how elusive information (notably detailed diagrams or photographs) can be for this species. It does match reasonably well observations in the Russian literature (Vinogradova 1974; unfortunately I have a low quality copy of this work and the images are blurry). This species was previously in a genus with Capsosiphon fulvescens (C.Agardh) Setchell & N.L.Gardner, but moved to Pseudothrix by Hanic & Lindstrom (2008). Although consistent with morphological observations, the molecular data available in support of this move were limited, especially for Capsosiphon fulvescens (C.Agardh) Setchell & N.L.Gardner. Additional phylogenetic study is warranted for both genera within the wider Ulotrichales. In addition, many more collections, as well as additional molecular data, are necessary to better characterize both of these species in terms of identification, possible cryptic diversity and ecological and biogeographical distribution.

Image A. Press of a small tuft of tubes from low intertidal on rock, Harrington Cove exposed biodiversity site, Grand Manan, NB (GWS003757).

Image B. Cells near the base develop as descending attachment rhizoids (GWS003757; rehydrated from press).

Image C. Cells lower on the tube are clearly organized in groups of 2-4 and are separated by visible indents (arrows) in the surface (GWS003757; rehydrated from press).

Image D. Cells are angular, irregularly distributed (some groupings of 2-4) and well spaced in the mid to upper thallus (GWS003757; rehydrated from press).

Image E. Cross section mid thallus (GWS003757; rehydrated from press).