British distribution: Generally common on rocky shores, but largely absent from the south-east (Hardy & Guiry, 2006).
This is one of the largest of our red seaweeds, and is remarkable in having frond blades, several centimetres in length, that resemble the leaves of trees, even to the existence of a midrib and pairs of lateral veins. The blades develop laterally from stalks that are themselves remains of midribs of former blades, the whole frond arising from a disc-like holdfast. The margins of the blades are sinuately lobed, sometimes deeply so, and also often somewhat toothed. Although an unusual and distinctive species, it can resemble rather battered growths of Delesseria sanguinea, in which the blade margins lack lobes or teeth and in which the midribs are more rigid and the numerous pairs of lateral veins are much more conspicuous.
The life history is an isomorphic alternation of generations, i.e. with morphologically similar diploid and haploid generations, the haploid (gametophyte) generation consisting of separate male and female plants. Details of sexual reproduction in the Rhodophyta, including the production of non-flagellate, spherical protoplasts as spermatia, and the production of similar meiospores from tetrasporangia borne on the diploids (sporophytes), are described in textbooks such as van den Hoek et al. (1995). Other specifically red-algal characteristics, such as the pit-plugs between cells and the non-stacked thylakoids of the chloroplasts, are also described in this work.
Like most of the red seaweeds, Phycodrys rubens occurs below the low-tide mark, where its accessory pigment, phycoerythrin, which masks the green of its chlorophyll, efficiently absorbs the longer-wavelength blue and especially the green wavelengths of light. These wavelengths penetrate some distance into sea-water but are not efficiently absorbed by chlorophyll, and so would not be used for photosynthesis without this accessory pigment.
The holdfasts may be attached to bedrock and boulders, shells, or, very often, to the stipes of the large, brown seaweed, Laminaria hyperborea, that forms kelp-beds below LTM on rocky shores.
Photographs: of cast-up and somewhat battered material, Great Cumbrae, April 2009.