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Why can’t we have flowers that bloom all year?

If we have evergeen trees are green all year why can’t we have flowers that bloom all year?
Archie Parker from Warwickshire (age 5-14)

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2 Responses

  1. Leaves are for photosynthesis – capturing the sun’s energy and converting into a useable energy form for the plant. Evergreens can therefore photosynthesise throughout the year as the sun is present 12 months of the year in most places on Earth. However, deciduous trees only have leaves and photosynthesise during the spring/summer time of the year – not too dissimilar to flowering times!

    Flowers are for reproduction, they are needed to produce and bring together the male and female sex cells (pollen and ovum). Ripe pollen and eggs must be produced at the same time by the same type of plant to allow fertilisation to take place. This often involves pollinators such as bees other insects and birds, which may be around only at certain times of the year. It is a good adaptation therefore to have flowers around when the pollinators are there too. After fertilisation of the egg with the pollen there needs to be a time when the seed is produced. All this takes time and energy which the plant gets from photosynthesis. So there is a link between energy from photosynthesis and the ability to flower and set seed.

    In some countries, closer to the equator where the seasons especially winter are not so pronounced, plants can photosynthesise and flower throughout the year, such as the oil palm. So you can have plants with leaves and flowers at anytime throughout the year. Even in this country the yellow gorse bush flowers throughout the year, although this is not common to many UK species.

    I wonder what effect global warming will have on photosynthesis and flowering times?

  2. Plants receive signals from the environment as well as other organisms, which influence their behaviour. For many plants this is a crucial stage in their life (for annual plants it means the beginning of the end, as they die after flowering). The main point of flowering is to produce seed and offspring for the next generation. So, it is important to choose the time correctly, rather than just flower at any random time. If conditions aren’t good, then all the resources that the plant uses will be wasted if conditions are not right for the seeds produced to mature. It is also a lot of work to make flowers, so it is probably not a very good strategy for the plant to make flowers all the time.

    Most plants can sense light (sensing its intensity, quality and duration). Daylength especially influences when plants choose to flower, and is sensed by the leaves of plants. This is called “photoperiodism”. The signal sensed by the leaves is transmitted around the plant and stimulates the plant to start to make flower buds. Some plants are “short day” plants (they flower in the autumn as the days are shortening), while some are “long day” plants, which flower in the summer, as the days lengthen. There are a few plants that are daylight insensitive.

    Proteins called phytochromes act as “receptors” for light, and translate the light signals within the plant cell. This influences the expression of several genes and proteins needed for stimulating flowering. Scientists have been trying to identify the genes involved in controlling flowering for a long time, but it has been very difficult; however several have now been identified.

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