Flowering plants need to get pollen from one flower to another, either within a plant for self-pollination or between plants of the same species for cross-pollination to occur. However, pollen can’t move on its own, so animals or the wind (and water in rare cases) move the pollen for plants.
Most New Zealand native flowering plants are animal pollinated – most by insects, but some by birds or even bats. Plants provide nectar and pollen as edible rewards to the animals for visiting a flower. As an animal reaches into a flower for its reward, it brushes against an anther, and some of the pollen sticks to its body. When the animal visits another flower, some of this pollen comes off onto the stigma – pollination has occurred. The pollen of animal-pollinated plants has a rough surface to help it stick to a pollinator.
Many flowers use colours to attract insects, sometimes helped by coloured guiding marks. Some have ultraviolet marks that can be seen by insects but are invisible to human eyes. Flowers are often shaped to provide a landing platform for visiting insects or to force them to brush against anthers and stigmas. The pōhutukawa (Metrosideros excelsa) uses colour in a different way. It only has very small petals but big bright red clusters of stamens.
Some flowers have scent to attract insects. Many of these scents are pleasing to humans too, but not all – some flowers attract flies with a smell of rotting meat. Colours can’t be seen in the dark, so scent is important for flowers that are pollinated by night-flying insects such as moths.
Bird-pollinated flowers tend to be large and colourful, so birds can see them easily against a background of leaves. Kōwhai (Sophora species), flax (Phormium tenax, harakeke) and kākā beak (Clianthus puniceus, kōwhai ngutu-kākā) are examples of bird-pollinated native plants. Some flowers even change colour to tell birds when to visit. The flowers of the tree fuchsia (Fuchsia excorticata, kōtukutuku) are greenish when ready for bird visitors, but after they have been pollinated, they turn red to tell birds to stop coming.
Most bird-pollinated flowers have lots of nectar, often at the bottom of a tube of petals. Birds need to brush against anthers and stigmas when reaching for the sugary reward with their long beaks. Some birds, such as tūī, stitchbirds and bellbirds, have special brush-like tips to their tongues to help them soak up the nectar.
Short-tailed bats can play an important role in the pollination of pōhutukawa, rewarewa (Knightia excelsa, New Zealand honeysuckle) and a hebe (Veronica macrocarpa). David Pattemore of Plant & Food Research found this out in recent studies on Little Barrier Island near Auckland.
Another plant pollinated by short-tailed bats is dactylanthus (Dactylanthus taylorii). This strange plant lives underground as a parasite on the roots of forest trees, with only the flowers poking up above the surface. The flowers have little colour but lots of nectar and a strong scent to attract the bats.
Grasses are wind pollinated, as are some of our native trees and shrubs, such as beech (Nothofagus species), kawakawa (Macropiper excelsum, pepper tree) and many Coprosma species. Pollination by the wind is very hit and miss. The wind may pick up pollen from a grass flower and scatter it all over the place. Only by chance will a little pollen land on another flower of the same species. To make up for this waste, wind-pollinated flowers produce a huge amount of pollen, as hay fever sufferers will know.
Wind-pollinated flowers tend to have small dull-coloured petals or, in the case of grasses, no petals at all. They don’t need petals, colour, nectar or scent to attract animals. The pollen grains are not sticky like those of animal-pollinated flowers, which reduces the chance of them sticking to leaves and other obstacles. The stigmas of receiving flowers are sticky in order to hold on to pollen carried by passing breezes.