Many plants can reproduce without sex. They do this by runners, bulbils, offsets and corms for example and we can do it artificially by taking cuttings but the problem with assexual reproduction is that it does not allow the importation of genes into the gene pool. It is better for plants to have genes from different sources so they can adapt to variations in climate, ecological disasters like flooding and perhaps develop resistance to diseases and pests. Therefore, the sex life of flowering plants is an important part of their life cycle, and it is this that flowering plants hope to achieve.
The purpose of a flower is to attract a pollinator in the hope that cross pollination will occur. Flowers are often adapted to attract a specific pollinator such as a bird, bat, moth (flowers open at might and are heavily scented). Many plants will self pollinate if a pollinator does not come before the flower fades but largely, it is better for sexual reproduction to occur and for this cross pollination is needed so flowers have developed scent, nectaries, bright colours and bear large amounts of pollen so make sure this process has a high likelihood of sexual reproduction (cross pollination) occurring.
When a flower is pollinated by an insect, bird, moth or animal even, pollen bearing the male gamete from another flower of the same species is deposited on the stigma of the female part of the flower. Plants can have hermaphrodite flowers or single sex flowers (monoecious flowers).
The stigma only allows pollen which is chemically compatible (ie from another flower of the same species) to germinate into its style (the tube, at the end of which is the receptive stigma).
On germinating, the pollen grows a long tube and this elongates down through the style until it reaches the ovary at the end of the style. The male gamete then travels along the pollen tube and to the ovary where it fuses with the female gamete or ova. The fused ova and pollen form a zygote and it is this which will develop into the seed and later a new plant.
After pollination, the style withers, the flower fades and tissues of the ovary and maybe other surrounding parts swell and develop into a fruit. This may be a seed pod, succulent fruit or a pome like a plum with a single large seed inside. Now sexual reproduction is complete and the seed is dispersed, by wind, animals, birds, water or simply by the fruit splitting to release the seeds.
So, the sex life of flowering plants is nothing exotic or exciting but it is important and plants do everything they can to ensure it is successful. For an annual, success in sexual reproduction and the formation of seeds is vital because once the plant dies, its entire progeny is left in the form of seeds.
Plants have a sex life and it is very different to that of animals, but amazing nonetheless..