The taxonomy, life history and ecology of some species of the Ceramiaceae (Rhodophyta) in the North-West Atlantic.

Three genera of the Ceramiaceae, Antithamnion Näg., Callithamniion C. Ag. and Plumaria Schmitz from the north west Atlantic were examined. Populations from insular Newfoundland were studied in the field, cultured, and cytologically examined to determine life histories and the factors inducing fertility. In addition a taxonomic re-assessment of the genus Antithamnion in the region is presented. -- A. Boreale (Gobi) Kjellm., A. pylaisaei (Mont.) Kellm. and A. americanum (Harv.) Farl. in Kjellm. Are morphologically indistinct and were studied in field and in culture to determine the degree of phenotypic variation. They are combined and transferred to Scagelia Wollaston as S. Pylaisaei (Mont.) nov. comb. Two genotypically distinct varieties are recognized; var. pylaisaei (Mont.) nov. comb. and var. boreale (Gobi) nov. comb. And var. boreale (Gobi) nov. comb., both have a Polysiphonia-type of life history with the addition of apomeiotic tetrasporangia on the gametophyte phase. Induction of fertility is independent of temperature or daylength. -- A. floccose (O.F. Mill.) Kleen is re-described and transferred to Antithamnionella Lyle. Plants remained sterile in culture, but field and cytological observations revealed no deviations from the Polysiphonia-type of life history. A fungal parasite of A. floccose is described as a new species Olpidiopsis antithamnionis Whittick and South. -- Voucher specimens for the occurrence in eastern Canada of A. cruciatum (C. Ag) Näg., A. plumula (Ellis) Thur. in Le Jol. And A. Pacificum (Harv.) Kylin, were examined. Only a single genuine specimen of A. cruciatum was located, most records being mis-identifications of S. pylaisaei. The records of A. pacificum are due to mis-identification of A. floccose. No material of A. Plumula could be located. -- The life histories of three species of Callithamnion; C. corymbosum (Sm.) Lyngb., C. tetragonum (With.) S.F. Gray and C. roseum sensu Harvey were investigated. C. roseum has a Polysiphonia-type of life history with no deviations, C. tetragonum is similar, but has monoecious gametophytes, and procarps and spermatangia were also observed on tetrasporophytes in culture. Only tetrasporangial plants of C. corymbosum were found, and in Newfoundland it reproduces by fragmentation. In all the species of Callithamnion the induction of fertility is temperature dependent, and C. roseum also requires long daylengths. -- Flumaria elegans (Bonnem.) Schmitz only occurs in Newfoundland as the triploid parasporangial generation, and fertility is controlled by water temperature