Due to its value , the life history of Porphyra has been extensively examined. The foliose flat blade that comprises the dominant growth form is haploid. Growth is during the colder parts of the year. During reproduction, the haploid plant produces spermatia along the borders of the plant. Although plants can produce either spermatia or carpogonia, generally a plant produces one or the other.
Plants producing spermatia appear to have a whitish margin that look as if the plant is old.
The tissue is a large array of cells that are producing colorless spermatia. Plants that produce carpogonia are in close position to those producing spermatia. The cells of the former that become carpogonia produce extensions that protrude above the surface of the plant. Fusion results in the production of carpospores which are diploid. These germinate often on oyster shells or other shell types producing a small filamentous stage termed the Conchocelis phase.