Individuals of Agarophyton vermiculophyllum are irregularly branched with terete axes (Image A). They can be difficult to differentiate from individuals of Gracilaria tikvahiae McLachlan characterized by terete axes. Axes in A. vermiculophyllum are terete throughout (Image A), whereas axes in Gracilaria tikvahiae McLachlan typically have flattened regions at the branching forks. Transverse sections in A. verimiculophyllum reveal medullary cells that are irregularly isodiametric in outline, 50-320µm in dimensions, and typically with thick and lamellate cell walls (Image B), grading to a 1-2 celled inner cortex and a distinct 2-3 celled outer cortex of oval to elongate cells 5-7.5µm by 10-15µm (Image C). In contrast, Gracilaria tikvahiae McLachlan transverse sections reveal typically larger and more irregularly shaped medullary cells lacking lamellate cell walls, as well as typically fewer outer cortical layers (1-2) of isodiametric rather than elongate cells.
An introduced species to our flora (see Saunders 2009), genetically verified records to date are sporadic north of Cape Cod, MA (Mathieson & Dawes 2017), which can further assist in identification. When in doubt, or in particular if reporting range extensions for A. vermiculophyllum molecular data should be generated (Saunders 2009).
Image A. Individual with irregular branching and terete axes from Haida Gwaii, BC, unattached in estuarine region (EGWS000148).
Image B. Transverse section displaying the typically isodiametric medullary cells with thick lamellate walls (mid intertidal on a shell in an estuary, Haida Gwaii, BC; GWS031331).
Image C. Transverse section closeup of the 2-3 layered outer cortex composed of oval to elongate cells (GWS031331).