MORPHOLOGICAL VARIATION IN 3 SPECIES OF THE GENUS CERAMIUM (CERAMIALES, RHODOPHYTA) FROM HAWAII - DIFFERENCES BETWEEN REPRODUCTIVE PHASES AND PHENOTYPIC PLASTICITY

The genus Ceramium Roth shows a high degree of morphological variability within some of its species. As reported in several descriptions, this variability has been experimentally examined in only a few cases where it has been shown to be the result of environmental influences or, it has been detected between tetrasporophytic and gametophytic generations. In order to examine the effect of environmental factors upon the morphology of different phases of the life cycle of the genus, three conspicuous species from Hawaii were cultured under controlled conditions and compared with field-grown plants. Ceramium clarionensis Setchell et Gardner, Ceramium flaccidum (Kutzing) Ardisonne and Ceramium sp. 1 showed different results for a number of characters assessed under the same conditions. Ceramium sp. 1 has a uniform morphology between gametophytes and tetrasporophytes while in C. clarionensis the phases are morphologically distinguishable. Ceramium flaccidum retains its self-defining character, the arrangement of cells in the node, in spite of the growing conditions. No comparisons between sexual and asexual phases were done in this species. However, the three cultured species show differences in their morphological characters from plants grown in the field, indicating their susceptibility to environmental factors. These results indicate the variability of responses within the genus and suggest the necessity to treat each species separately.