A lavender field near Provence, France.
Flowering is the process by which higher plants transfer male gametes to female organs thereby uniting two sets of chromosomes and increasing natural diversity. During the formation of male and female gametes, slight changes take place in chromosome structure. Consequently, the resultant next generation differs slightly from its parents. That is the stuff on which natural selection operates.
Useful variations increase the survival fitness of some offspring, while individuals with disadvantages wither and die. Charles Darwin recognised the power of natural selection for the environmentally fittest individuals and how that leads eventually to species evolution. Succeeding generations of scientists have discovered details of the processes involved and how these may result in more useful plants for humankind by plant breeding.
Transferring the male gametes (i.e. pollination) happens by a variety of mechanisms which are suited for the environment in which particular plants grow. At its simplest, pollen which consists of cells containing male gametes is transferred within the same flower. That is suitable for plants growing in for example, alpine environments where few other options exist.
Pollen grains contain both reproductive and non-reproductive cells.
Cross-transfer of pollen from one flower to another is achieved either by physical means such as wind or water, or by partnerships with animals – particularly insects and especially bees. Wind transfer is suitable for trees such as hazel, birch and willow, which flower ahead of leaf formation in the early spring when it is too cold for insect flight. Biologically, it is a wasteful mechanism because much of the pollen does not reach its target.
Cross-pollination by insects produces by far the most colourful and exuberant flowers. These have evolved brilliantly colourful displays and intricate mechanisms suitable for either general interaction with insects or as means for partnership. These relationships have co-evolved and converged over numerous generations meeting the needs of both parties.
Sexual reproduction in plants. Video: FuseSchool - Global Education
Plant scientists are presented with intriguing questions in understanding how these relationships could have developed. On the practical side, plant breeders are presented with enormous opportunities for developing massive arrays of new varieties, particularly with ornamentals such as the garden favourites like dahlias, chrysanthemums, lilies and roses.
Enormous international trade has developed over the last hundred years exploiting increasingly colourful flowering plants.
An estimated 24% of Europe’s bumblebees are threatened with extinction.
Cross-pollination is absolutely vital for many field vegetable crops, especially peas and beans and the top and soft fruits. A reduction in beneficial insect populations now presents dire threats for natural biodiversity, our food supplies and the enjoyment of ornamentals.