Flowers and Pollinators

The aim of flowers is sex, plants invest a huge proportion of their energy into producing flowers to ensure that pollen is passed from the male part (anthers) to the female receptive part (stigma) either to the same floer, another flower on the same plant (self pollination) or to flower on another plant of the same species (cross pollination).

Wind pollinated flowers do not need to be elaborate as their pollen is transferred from flower to flower by the movement of the air. Their only problem is to ensure that some of the pollen lands on a receptive flower so they produce lots of it and have many flowers. The flowers are inconspicuous as they do not need to attract a vector – something used to carry the pollen from flower to flower.

However, flowers which rely on vectors to pollinate them such as an insect, bird, moth or other animal, need to attract them. One way they do this is to provide food. Some flowers provide food in the form of waxy sweet pollen grains which attract beetles and flies who feed on them and in turn carry grains of pollen from flower to flower (those they do not eat). Others provide nectar which also has a sweet smell and attracts vectors by scent. They may also secrete aromatic oils in the petals which serve to tell the vector that food is available (and pollination required). The insect, bird or moth comes, feed and unwittingly pollinates the flowers.

However, many plants rely on specific pollinators and have evolved elaborate flowers to ensure the right pollinators come to them, know when they are ready to be pollinated and to ensure success. They therefore produce elaborate, showy, colourful flowers which will attract particular groups of vectors. Also, some plants grow deep in rain forests, high in mointains or in other areas where few pollinators fly and for these plants, attracting pollinators quickly during the short flowering season is a must. Therefore, many alpines, desert plants and forest epiphytes have elaborate, large and colourful flowers which ensure they attract the pollinators.

Many will have colours in a particular hue which attract certain insects. Bees, for example are attracted to blues, birds to reds and pinks and moths to creams and yellows. Along with the colour, many flowers have pollen ‘pathways’ which, to an insect’s eye, act as a runway to direct them to the nectaries (where they have to pass the anthers and stigma and pollinate the plant in return for a food reward). Many flowers, as well as being brightly coloured, are of a particular shape to enable the pollinator to feed and pollinate effectively.

Swet peas, elaborate and showyt though they are have adapted not for our pleasure but to ensure pollination by bumble bees. Only the weight of a few bee species can make the heel or landing petal drop down to reveal the nectaries, anthers and stigma and these in turn are located so the bee brushes the anthers on the way in and the stigma on the way out, thus making sure self pollination is avoided and cross pollination more likely (this is more beneficial to the plant as it allows genetic variation).

Some flower, for example, have downturned heads with large flowers and deep nectaries. These attract hummingbirds, or butterflies and moths which use their long proboscis or tongues to reach the nectaries hidden deep within the flowers and so carry out pollination in the process. Some even open at night releasing gorgeous scents to attract moths which fly at night or even, in some cases, certain species of bat.

Plants are highly evolved organisms and those with elaborate flowers have developed to ensure they get pollinated by their specific vector. The flowers are coloured to attract, scented to tell the vector food is available and their internal anatomy is just right for the particular favoured vector. Flowers of elaborate form tend to be fewer innmber than those relying on wind or water but more energy goes into each flower from the plant and the investment is worth it because this highly evolved relationship between elaborate flowers and pollinating vectors works.

Once again, plants show us how it is done.