NEW OBSERVATIONS ON THE TILOPTERIDACEAE (PHAEOPHYCEAE) .1. FIELD STUDIES OF HAPLOSPORA AND PLAEOSIPHONIELLA, WITH IMPLICATIONS FOR SURVIVAL, PERENNATION AND DISPERSAL

Two of the three monospecific genera in the Tilopteridales, Tilopter i s and Haplospora, are rare but widely distributed in the North Atlanti c, whereas Phaeosiphoniella is known from only five localities in Newf oundland. Field observations were performed over several years in an u nstable habitat with abundant Haplospora and Phaeosiphoniella. Seasona lity of the populations reflected the local environmental conditions w hich permitted uprights to appear only in winter al temperatures below 5 degrees C and low irradiances. Survival over the summer depended on prostrate crusts sometimes consisting of several hundred contiguous d iscs, each derived from the apical growth of rhizoids. Substrata such as scallop shells were found to carry numerous crusts which constitute d the main holdfast system from which new uprights were produced in wi nter. Reproductive structures in Phaeosiphoniella were mostly absent a nd propagation depended exclusively on fragmentation, while Haplospora showed an alternation of generations. Members of the Tilopteridaceae are assumed to be relict species, especially Phaeosiphoniella which ex ists only at a few locations. Presumably all three species have weak c ompetitive capabilities but can survive, due to their crusts, in physi cally disturbed habitats on small-sized substrata with certain refugia l characteristics.