The ploidy levels are determined by understanding the life cycle stages. In bryophytes (moss, liverwort), the gametophyte is the dominant haploid phase. The protonema develops from a spore (produced by meiosis), and leaf cells are part of the gametophyte—both are haploid. Gemmae are vegetative propagules on the gametophyte thallus, hence haploid. The ovum is a gamete, always haploid. In pteridophytes (fern), prothallus is the gametophyte (haploid), while zygote is diploid as it develops into sporophyte after fertilization. In angiosperms, the plant body is diploid sporophyte (meristem cells are diploid), but endosperm is triploid due to double fertilization—fusion of one male gamete with two polar nuclei.