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Studies seasonal and between-plant variability in the morphology of Sargassum mathiesonii species nov. (Phaeophyta) from the Gulf of Mexico. Patterns of morphological variation; Phenology; Vescile length; Blade length; Attribution of anatomical variation primarily to ontogeny.

Phenotypic and ontogenetic changes in apparent photosynthesis and dark respiration for Sargassum poly-ceratium Mont were related to the differential allocation of resource into blades, stems, vesicles, and fertile branches as well as anatomical parameters of surface area, volume, and blade density a population in the Content Keys, Florida. Three divergent phenotypes were evaluated during four phases of ontogeny: maximum growth (October), peak reproduction (December). senescence (April), and stasis (July). Photosynthetic and respiratory rates changed throughout the year, at different stages of morphogenesis and among different phenotypes. Photosynthesis was highest during active growth, decreased during reproduction and senescence, and was lowest during stasis. In contrast, respiration was higher during peak reproduction and stasis. Temporal phenotypic, and ontogenetic changes in apparent photosynthesis were best explained by interactions among anatomical features, growth stages, and source-sink relationships of metabolic reserves and pigments. Surface area :volume (SA:V) ratios played a secondary role. Photosynthetic performance of mature axes decreased with the allocation of resources away from blades to air bladders and fertile branches. Apparent productivity and development of fertile branches on phenotypes were not rorrelated. High respiratory rates, SA:V ratios, blade areas, and low blade densities occurred on developing axes and were consistent with adaptations to low light fields. Sargassum polyceratium because of its morphological differentiation, is a relatively complex. physiologically variable alga. [ABSTRACT FROM AUTHOR]

Temporal variability in certain morphological and taxonomically important features was quantified for Sargassum polyceratium Mont. From a population in the Content Keys. Florida (U.S.A.). patterns of blade development, senescence, and loss caused pronounced seasonal changes in blade length-width ratios. Blade length and width were maximal early in the growing season (August-November) and decreased as the annual stems matured. Early in the growing season, plants had broader bblades with randomly distributed cryptostomata. Late in the growing season (February-April), plants had more linear blades with cryptostomata approximately arranged in two rows, one on each side of the midrib. The length-width ratio of blades increased acropetally along the stems and were directly correlated to the size of the cryptostomatal opening and inversely correlated with the number of cryptostomata. The branching pattern of the annual stems ranged from short spur branches to well-developed, lateral axillary branches. The frequency of bifurcated blades increased singnificantly late in the growing season. Vesicle shape and size and pedicel length were temporally stable. Alated pedicles and mucronate vesicles occurred in low frequencies. The variability of the morphological features used to delineate species within the genus Sargassum on the tropical eastern coasts of the Americas is poorly understood. [ABSTRACT FROM AUTHOR]