Experimental observations on variability of leaf and air vesicle shape of Sargassum muticum

Abstract

Seasonal variations in the range of air vesicle and leaf shape upon the brown alga Sargassum muticum (Yendo) Fensholt provide some discrepancies with descriptions of material from the alga's indigenous Japanese and introduced British Columbian habitats.Experimental observations indicate that mucronate air vesicles are most common at low (i.e. 10 °C) and high (i.e. 25 °C) temperatures, with those of 30 °C being injurious to plant growth. Air vesicles with spiked proliferations are also seen to increase in occurrence with an increasing light intensity at 20 °C. Excised ‘winter’ form leaves collected in February were able to regenerate ‘summer’ form leaves from their damaged bases, under culture conditions.Field and laboratory investigations show that leaf and air vesicle shape tend to vary seasonally and may be experimentally changed by both temperature and light intensity. Such plasticity observed in the morphology of these characters in S. muticum raises doubts as to the taxonomic status of many species ascribed to the large genus Sargassum.