Chorda filum (Linnaeus) Stackhouse (A)

This species is quite distinct in our NW Atlantic flora. Individuals are unbranched brown tubes 20-300 cm long and 3-6 mm wide (Image A). Except for the short stalk the thalli are covered with clumps of colourless phaeophycean hairs (Image B), which give the plants a haloed appearance (Image C). In section there is a heavily pigmented outer cortex, an inner cortex of relatively large isodiametric thick-walled cells surrounding a medulla which varies from sparsely filamentous to hollow (Image D).

We have genetically verified records from throughout Atlantic Canada (including Gulf of Saint Lawrence, QC), but not from Labrador (we have sampled central and northern Labrador, but not the southern region). All collections from central Labrador and into the Canadian Arctic and beyond are a recently segregated species Chorda borealis H.Kawai, T.Hanyuda & G.W.Saunders. We have collections from mid intertidal pools to 10 m subtidal, the sporophyte being annual with our collections falling between June and October. Confusion with another ‘shoestring’ alga, Halosiphon tomentosus (Lyngbye) Jaasund could occur, but the hairs in that species are heavily pigmented giving that species a dark fuzzy covering rather than the clear haloed appearance of the Chorda species in our waters.

image.pngImage A. Individuals growing in a mid intertidal pool on rock (Bergen, Norway; GWS038013).

Image B. A view of a clump of the colourless multicellular phaeophycean hairs on the surface of a drift individual collected at Shediac, NB (GWS044429).

Image C. Dense covering of colourless hairs on the surface give this species a haloed appearance (subtidal (1 m) on rock, Whycocomagh Picnic Area Site #1, bras d’Or Lake, Cape Breton, NS; EGWS001133).

Image D. Partial cross section displaying the pigmented outer cortex (top), inner cortex of large isodiametric cells, and a hollow medulla with some sparsely distributed medullary filaments (GWS044429).