Fig. 1

Isomorphic biphasic (haploid-diploid) life-cycle of Gracilaria chilensis. a Life cycle showing the free-living tetrasporophytes (diploids) and dioicious gametophytes (haploids, male and female) stages. Tetrasporophyte, when mature produce haploid tetraspores after meiosis and release them to the environment. Tetraspores settle and grow into adult male or female gametophytes. The gametophyte males release gametes that fertilize female gametophytes. From the fertilized oogonia, a short-lived diploid epiphytic stage (the carposporophyte) develops on the female thallus. Within each carposporophyte, the zygote undergoes successive mitoses allowing to produce many thousand of carpospores that are then released into the environment, where they settle and grow into diploid tetrasporopytes. b Mature male bearing gametocysts (i.e., ovate white spots). Male gametes are released in the water column. c Mature tetrasporophyte thallus with tetrasporocysts (i.e., structures where tetraspores are produced) visible. Deep red pigmented tetrasporocysts still contain tetraspores while round white spots correspond to empty tetrasporocysts. d Female thallus after fertilization bearing carposporophytes. e Detail of a carposporophyte liberating carpospores. All photographs by Paula Valenzuela