Evolutionary Origins
The evolutionary origins of double fertilization and endosperm are unclear, attracting researcher attention for over a century of research. describes the two major hypothesis:
- The double fertilization initially used to produce two identical, independent embryos ("twins"). Later these embryos acquired different roles, one growing into mature organism and another merely supporting it. Hence the early endosperm was probably diploid, same as another embryo. Some gymnosperms, such as Ephedra, do may produce twin embryos by double fertilization. Any of these two embryos are capable of filling in the seed but normally only one develops further (another eventually aborts). Also, the most basal angiosperms still contain the four cell embryo sac and produce diploid endosperms.
- Endosperm is the evolutionary remnant of the actual gametophyte, similar to the complex multicelular gametophytes found in gymnosperms. In such case acquiring the additional nucleus from sperm cell is the later evolutionary step. This nucleus may provide the parental (not only maternal) organism with some control over endosperm development. Then becoming triploid or polyploid are later evolutionary steps of this "primary gametophyte". Nonflowering seed plants (conifers, cycads, Ginkgo, Ephedra) form a large homozygous female gametophyte to nourish the embryo within a seed.
Read more about this topic: Endosperm
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