Culture and field study ofStilophora rhizodes(Phaeophyceae, Chordariales) from Nova Scotia, Canada

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Abstract
The life history of Stilophora rhizodes has been completed in culture using zoids from both unilocular and plurilocular sporangia of macrothalli from Pomquet Harbour in the southern Gulf of St. Lawrence, Nova Scotia, Canada. Zoids from unilocular sporangia developed into haploid microthalli at 0, 5, 10, 15, 20, 24 and 28°C which in turn developed plurilocular zoidangia at 5–24°C. At or below 10°C zoids released by microthallic plants acted as gametes to produce diploid macrothalli or settled individually to produce haploid macrothalli or haploid microthalli. At 15°C or higher, zoids settled and developed only into haploid microthalli. Plurilocular sporangia on field macrothalli and on precociously fertile macrothalli in culture released zoids which settled and grew directly into macrothalli. Juvenile macrothalli developed normally below 15°C but became irregular at higher temperatures. Stilophora rhizodes macrothalli in Pomquet Harbour produced mostly unilocular sporangia in summer and plurilocular sporangia when the water temperature was falling in autumn. Juvenile macrothalli were found in the field in spring and autumn. Microthalli, juvenile macrothalli and fragments of mature plants are all capable of overwintering at 0°C. Chromosome counts indicated that N = 15±1, and 2N = 30±2.