Branching pattern of gametophytes and tetrasporophytes of Ceramium codicola (Ceramiales, Rhodophyta) is related to phase and reproductive structures

Abstract

Branching of tetrasporophytes and gametophytes of Ceramium codicola was characterized by the Strahler method of ordering branches and by measuring angles of ordered branches in order to quantify differences in morphology between these ‘isomorphic’ reproductive stages. Numbers of ordered branches varied between the stages, with female and male gametophytes having more first-degree branches than tetrasporophytes, and male gametophytes having more second- and third-degree branches than females or tetrasporophytes. Males also had more branches and more orders of branching at the site with higher wave action. Ratios of branches of adjacent orders revealed patterns that were more consistent. The ratios of 1°:2°, 2°: 3°, and 3°: 4° branches for male gametophytes and tetrasporophytes were about 2.5, whereas female gametophytes had higher ratios of 1°: 2° and 2°: 3° branches. This indicates that female gametophytes have a greater number of first- and second-degree branches that arise apart from dichotomous branching. The similarity of male gametophytes and tetrasporophytes could be explained by the fact that spermatia and tetrasporangia are produced along the mature branches of thalli of these reproductive stages. Thus, thalli with more first-degree branches would tend to have a reduced production of reproductive cells. In contrast, carpogonia are produced near the tips of first-degreebranches, so having more first-degree branches would result in a greater potential for reproductive production. The angle of branching was somewhat different between reproductive stages, with females having greater angles where second-degree branches meet than males or tetrasporophytes. Female and male gametophytes were twice as wide as tetrasporophytes when comparing segments of comparable length. Thus, gametophyte and sporophyte phases appear to differ in the width of thalli, although this does not appear to be due solely to increased branching angles.