Red algae are the most diverse group of seaweeds on temperate shores.  Colors can range from rose red or maroon to dark red, brown, or even green depending on relative concentrations of photosynthetic pigments (chlorophyll, phycoerythrin, phycocyanin, allophycocyanin).  Pink coralline red algae grow as hard flat crusts or jointed erect forms; as their name implies they deposit calcium carbonate in their cell walls, presumably as a defense against grazers.

Red algal life histories are complex and typically comprise three stages: a diploid tetrasporophyte that undergoes meiosis to produce haploid tetraspores, which are released and settle to grow into haploid male or female gametophytes.  Gametophytes may look identical or very different (heteromorphic) from the tetrasporophyte phase from which they arose.  Males and females produce gametes via simple mitosis; males release non-motile spermatia which find and fertilize ova that are retained by the female.  The fertilized diploid zygote grows into the third generation, the carposporophyte, firmly attached to the haploid female.  Eventually, the carposporophyte releases diploid carpospores that grow into tetrasporophytes and the cycle begins again.