Autecological studies of the genusPorphyra

The type of Porphyra umbilicalis (L.) J. Ag. is recognised and the species may be regarded as widespread and adaptable. In Britain, three distinct forms can be marked out but these appear to be responses to particular ecological conditions. Early in development, formation of well-formed, pigmented spores takes place over large areas at the edge of a thallus, though no fertilisation has been seen in British specimens. In culture, these spores are shed in considerable numbers and germinate readily, giving rise either to a filamentous conchocelis-phase or to dwarf plantlets. Both phases are capable of reduplication by monospores and both appear to be perennating stages in the life-cycle capable of giving rise to macroscopic plants under certain conditions.