The green algae exhibits three types of life cycles:
(i) Haplontic (ii) Diplontic (iii) Diplohaplontic
(i) Haplontic :
(a) The dominant phase is haploid, while diploid stage is present only in the form of zygote or zygospores.
(b) Meiosis occur at the time of zygote germination e.g. Chlamydomonas, Ulothrix, Spirogyra.
(a) The dominant phase in the life cycle is diploid.
(b) Gametes are produced through meiosis.
(c) They represent haploid phase.
(d) The diploid phase is restored as a result of fusion of gametes, e.g. Caulerpa.
(a) In this life cycle, both diploid and haploid phase are well developed and multicellular.
(b) They are respectively called sporophyte and gametophyte.
(c) The haploid gametophyte produces haploid gametes, which fuse into diploid zygote.
(d) The diploid zygote grow into a diploid sporophyte. The latter produce haploid spores or meiospores through meiosis.
(E)New gametophytes are produced by the germination of meiospores.
(f) Thus, this cycle exhibits alternation of generation, between haploid and diploid multicellular generations.