Morphological and biosystematic studies of Gelidium pusillum and G. pulchellum (Gelidiaceae, Rhodophyta) from Europe

The marine red alga Gelidium pusillum sensu Dixon et L. Irvine (Gelidiaceae, Gelidiales) in Norway, the British Isles and northern France is shown to include at least two morphologically variable species: G. pusillum (Stackhouse) Le Jolis, a mator turf-forming entity found in the upper and mid intertidal on open rock, and G. pulchellum (Turner) Kützing, a mid and lower intertidal rock-pool inhabitant that grows in loose clumps or tufts. Lectotypes for the basionyms of both entities are selected. North-eastern Atlantic isolates of both species show a Polysiphonia-type life history in laboratory culture. Interfertile isolates of G. pusillum from Norway, Wales, Ireland and France did not cross in laboratory culture with interfertile isolates of G. pulchellum from the west coast of Ireland and from France. However, some isolates of G. pusillum and G. pulchellum, particularly those from the Mediterranean, did not reproduce in culture, and could not thus be tested for crossability. At photon irradiances of 50–350 μmol m−2 s−1, the optimum temperature for growth in G. pusillum from France is 23°C whereas that of G. pulchellum from Ireland is 20°C. In both isolates growth increases with increasing irradiance. Preliminary starch gel electrophoresis for the isoenzymes PGI and SOD in the Atlantic and Mediterranean cultured isolates provide further evidence that G. pulchellum and G. pusillum represent distinct entities at the species level.