On the expression of phenotypic variability: why is Sargassum so taxonomically difficult?

Anatomical and physiological variation is inherent in all living organisms, originating at both thegenotypic and the phenotypic levels. In the morphologically complex phaeophyte Sargassum,characters exhibit variability on several scales: (1) temporal, (2) intraindividual, (3) interindividual, (4)environmental, and (5) interlocality (geographical). Taxonomic inconsistencies result from haphazardmeasurements of variation and from species descriptions that describe only part of the plant'sanatomical range. Prominent features, such as blade shape and size, are used almost exclusively todistinguish taxa but are highly variable. Polymorphs increase between-plant variation and, in somecases, make species descriptions inadequate. The search for stable characters or suites ofcharacters is further complicated by developmental cycles, low-occurrence traits, environmentalvariates (polymorphisms and polyphenisms), and genetic differences among populations. Variationat the phenotypic and genotypic levels must be understood before an acceptable species conceptcan be developed.