The genus phymatolithon in the Gulf of Maine

New information on anatomy, cytology and the development of reproductive structures is presented to show that Phymatolithon is a genus distinct from both Clathromorphum and the branching members of Lithothamnium . Also, a new species of Phymatolithon , Ph. rugulosum , is described. The reproductive cycles and geographic and bathymetric distributions of Ph. laevigatum and Ph. rugulosum in the Gulf of Maine are presented and discussed. There is strong indication that the geographic distribution of crustose corallines in the region is controlled primarily by maximum summer temperatures. The depth distributions are apparently controlled primarily by decrease of light with depth, though temperatures and substrate are also factors.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42883/1/10750_2004_Article_BF00170412.pd