Haplodiplontic

Haplodiplontic refers to a life cycle in which two multicellular generations alternately occur: a haploid gametophyte and a diploid sporophyte. In this arrangement, the gametophyte produces haploid gametes by mitosis, and fertilization between compatible gametes forms a diploid zygote that grows into the sporophyte. The sporophyte, in turn, produces haploid spores by meiosis, and these spores develop into new gametophytes, completing the cycle. Thus, both the haploid and diploid phases are multicellular and alternation of generations characterizes the life history.

In plants, haplodiplontic life cycles are widespread and can vary in which generation is dominant. In bryophytes (mosses, liverworts, hornworts), the gametophyte—haploid and often dominant—is the conspicuous, long-lived stage, while the sporophyte is typically dependent on the gametophyte for nutrition. In pteridophytes (ferns and their relatives) and especially in seed plants (gymnosperms and angiosperms), the sporophyte is the dominant, free-living generation, and the gametophyte is usually reduced and often dependent on the sporophyte. In seed plants, the male and female gametophytes are highly reduced and develop within the sporophyte’s tissues.

Haplodiplontic life cycles are a defining feature of embryophytes (land plants) and reflect the evolutionary diversification of plant reproduction. The balance between the two generations influences life history traits, ecological strategies, and the manner in which plants adapt to different environments.