<P> The term is also used in botany to describe the phenomenon of seedlings emerging from one embryo . Around 20 genera of gymnospores undergo polyembryony, termed "cleavage polyembryony," where the original zygote splits into many identical embryos . In some plant taxa, the many embryos of polyembryony eventually gives rise to only a single offspring . The mechanism underlying the phenomenon of a resulting single (or in some cases a few) offspring is described in Pinus sylvestris to be programmed cell death (PCD), which removes all but one embryo . Originally, all embryos have equal opportunity to develop into full seeds, but during the early stages of development, one embryo becomes dominant through competition, and therefore the now dormant seed, while the other embryos are destroyed through PCD . </P> <P> The genus Citrus has a number of species that undergo polyembryony, where multiple nuclear - derived embryos exist alongside sexually - derived embryos . Antonie van Leeuwenhoek first described polyembryony in 1719 when the seed in Citrus was observed to have two germinating embryos . In Citrus, polyembryony is genetically controlled by a shared polyembryony locus among the species, determined by single - nucleotide polymorphism in the genotypes sequenced . The variation within the species of citrus is based on the amount of embryos that develop, the impact of the environment, and gene expression . As with other species, due to the many embryos developing in close proximity, competition occurs, which can cause variation in seed success or vigor . </P>

In which gymnosperm embryo sac polyembryony is present