This is the life cycle in which the haploid phase is followed by two successive diploid generations.
In plants like Polysiphonia the haploid plant (gametophyte) produces diploid zygote after gametic fusion. This zygote produces a diploid carposporphyte on the gametophytic plant. This carposporophyte produces diploid carpospores. These carpospores are liberated and they germinate to form the diploid tetrasporophyte which is an independent plant. This produces tetrasporangia where meiosis takes place and produces haploid tatraspores. They germinate to form the haploid gametophyte. This is called the diplobiontic life cycle.