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Floral color change occurs in flowers in a wide range of
angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit ...
taxa that undergo a color change associated with their age, or after successful
pollination Pollination is the transfer of pollen from an anther of a plant to the stigma (botany), stigma of a plant, later enabling fertilisation and the production of seeds. Pollinating agents can be animals such as insects, for example bees, beetles or bu ...
.


History

The first written record of the term ''floral color change'' was in 1877 when
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...
(12 February 1809 – 19 April 1882) forwarded a letter from his colleague, naturalist
Fritz Müller Johann Friedrich Theodor Müller (; 31 March 182221 May 1897), better known as Fritz Müller (), and also as Müller-Desterro, was a German biologist who emigrated to southern Brazil, where he lived in and near the city of Blumenau, Santa Cata ...
(31 March 1821 – 21 May 1897) to the British multidisciplinary science journal, ''
Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...
''. Müller documented the patterns and efficiency of pollination in relation to the floral color change that occurred in ''
Lantana ''Lantana'' () is a genus of about 150 species of perennial plant, perennial flowering plants in the verbena family, Verbenaceae. They are native to tropics, tropical regions of the Americas and Africa but exist as an introduced species in num ...
'' flowers found in Brazilian forests. It is now understood that floral color change has evolved independently several times and has maintained morphological and physiological differences across taxa. Although this phenomenon was first mentioned over 200 years ago, research on its biological relevance has only occurred within the last few decades.


Mechanisms

The three major pigments involved in floral color change are
anthocyanin Anthocyanins (), also called anthocyans, are solubility, water-soluble vacuole, vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart named a chemical compou ...
s,
carotenoid Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...
s, and betalains. Color changes can occur from any of the following; an accumulation or loss of anthocyanins, accumulation or loss of carotenoids, or an accumulation of betalains. Floral color change may also be caused by an increase or decrease in pH causing a reddening/blueing of anthocyanins and co-pigments. Floral color change can be inducible or non-inducible. Some flowers will change color at the same rate regardless of pollinator visitation, while others can be induced by pollen deposition on the stigma. However, inducible flowers will eventually change color due to
senescence Senescence () or biological aging is the gradual deterioration of Function (biology), functional characteristics in living organisms. Whole organism senescence involves an increase in mortality rate, death rates or a decrease in fecundity with ...
even without pollinator activity. Depending on the species, floral color change can affect an entire flower or it can occur in localized parts. Previous research has found that moth-pollinated flowers are more likely to have whole flower color changes, while other insect-pollinated flowers are more likely to have localized color changes.


Pollination

While flowers typically wilt after pollination, many angiosperm taxa maintain their flowers even after their sexual viability has come to an end. During this time, flowers that have been successfully pollinated and have reduced rewards may undergo color changes, which act as a signal to their pollinators. Insect pollinators preferentially visit flowers that are sexually viable and have not undergone color change. Pollinators will learn and discriminate against floral stages from these signals benefiting both parties by allowing insects to be guided to flowers that are rewarding, while the flowers receive pollination. It has been shown that the size of the plant's floral display is important in relation to plant-pollinator interactions. Larger floral displays are more likely to be seen and visited by their pollinators than small inconspicuous floral displays. Several angiosperm species are known to increase their floral display without producing additional flowers. These species accomplish this by retaining the older, nonfunctional flowers that would often be abscised in other species to reduce the cost to the plant that comes from the carbohydrates needed and the water loss that occurs when maintaining these tissues. However, when these flowers are retained on insect pollinated plants there are the potential benefits of enhanced reproductive success through increased pollen deposition on stigmas and export of pollen to fertilize the ovules of other plants.


Other forms of floral color change

Senescence is one of the main causes of floral color change along with induction by pollination. While angiosperm taxa show variation in the time that it takes senescence to occur, the mechanism is typically associated with the biosynthesis of anthocyanins. Evening primrose in the genus '' Oenothera'' are a common example of flowers that undergo color changes due to senescence. ''Oenothera'' will bloom in the evening and appear to be white or yellow, and by morning they fade to pink or orange. Floral color change can also be a result of an increase or decrease in pH. ''
Hydrangea ''Hydrangea'' ( or ) is a genus of more than 70 species of Flowering plant, flowering plants native plant, native to Asia and the Americas. Hydrangea is also used as the common name for the genus; some (particularly ''Hydrangea macrophylla, H. m ...
'' is a model genus for this particular chemical change in flowers. Floral pigments in ''Hydrangea'' are affected by the presence of aluminum ions in the soil, causing changes in flower color from red, pink, blue, light purple or dark purple. There has been one non-chemical example found within
Caesalpinioideae Caesalpinioideae is a botanical name at the rank of subfamily, placed in the large family Fabaceae or Leguminosae. Its name is formed from the generic name '' Caesalpinia''. It is known also as the peacock flower subfamily. The Caesalpinioideae a ...
, a single sub-family of
Fabaceae Fabaceae () or Leguminosae,International Code of Nomen ...
where the folding of
petal Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corol ...
s cause changes to the color patterns of the flowers.


See also

*
Seasons A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's axial tilt, tilted orbit around the Sun. In temperat ...


References

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