Ceramium: Life History
Ceramium life history cartoon.
Ceramium has a triphasic, isomorphic life history, with two diploid sporophyte phases and one haploid gametophyte phase. Starting with the tetrasporophyte phase, the alga undergoes meiosis and produces tetraspores, dark red spheres around the nodes, generally divided tetrahedrally. In some species the tetraspores are fully exposed on the surface of the plant, while in other species tetraspores are embedded in the cortex.
Tetraspores in the cortex of C. codicola
These tetraspores grow up into either male or female gametophytes, which have a similar appearance to the sporophytes. Male gametophytes produce colorless spermatangia from the cortical cells, which then release spermatia.
Drawing of spermatangia (small colorless ovals) growing out of cortex cells.
Female gametophytes grow three or four-celled carpogonial branches with long thin trichogynes made to catch the spermatia broadcast by the male gametophytes.
Drawing of carpogonial branches showing long trichogynes.
After fertilization, the carpogonial branch shrinks and the newly fertilized nucleus grows into the third phase, the carposporophyte. The carposporophyte is supported by small branchlets that grow after fertilization called involucral branches. In Ceramium, unlike in other red algae, the carposporophyte is not covered by a pericarp: protective, diploid female gametophyte tissue.
Drawing of a cystocarp with involcral branches
The carposporophyte phase remains on the female gametophyte and eventually releases carpospores. These carpospores grow into tetrasporophytes and start the cycle over again.
Drawings after Cho, T.O. et al. (2002).
© 2005 Lynn Asbeck