How does fertilization occur after pollinia reach an orchid stigma?

When pollinia reach an orchid stigma, the process of fertilization begins with the germination of pollen tubes. These tubes grow down through the center of the column to reach the developing ovules located in the ovary.1

This growth process is often accompanied by the sides of the stigma swelling to enclose the pollinia. The journey of the pollen tubes to the ovules typically takes six weeks or longer. Once the tubes reach the ovules, fertilization occurs, leading to the development of zygotes and eventually embryos.1

It is important to note that in many orchids, this process may be prevented by genetically controlled self-incompatibility, which acts as a mechanism to ensure genetic diversity by preventing pollen from fertilizing ovules with the same genetic combination.23