Most plants live their whole lives rooted in one spot and cannot move from place to place. When it is time to reproduce, they cannot go in search of a mate. Plants need agents like wind, water or animals to carry pollen containing the male reproductive cells from one flower to the female reproductive organs in another flower. This is called pollination. It is a vital stage in the reproduction of all seed-bearing plants.

Flower structure

What are genes?

• The Sorrels or Surings (Oxalis species) are brightly coloured flowers that grow in clumps from underground bulbs.
• A single Sorrel plant can form a clump of plants by vegetative reproduction. This means that all the flowers in a clump are genetically the same. We call these individuals that all have the same genes a clone.
• If pollen from one flower is transferred to another flower of the same clone, this is still considered to be ‘self-pollination’. So how do Sorrel plants avoid pollinating themselves?

Try this investigation

• They attract the attention of pollinators with colourful, patterned flowers that act like advertising billboards.
• They attract insects with a range of appealing smells.
• They offer pollinators rewards for their services.
• The structure of different flowers suits particular pollinators.

In this section we will find out how some of the plants on the poster are pollinated. Look for plants and pollinators in your neighbourhood and try to work out how flowers attract and reward their pollinators.

Different groups of animals see light and colour in different ways. We see colours ranging from red through yellow and green to violet, and call this the “visible spectrum”. Some animals are unable to see all the colours in our visible spectrum, but they can see some wavelengths of light that we cannot see (e.g. ultra-violet).

Most birds can see the colour red, but few insects can tell the difference between green and red. Bees can see ultra-violet light, which is invisible to birds and people.

Move your mouse over the picture to see how the bee may see this flower.

Sunbirds are small birds with long, curved beaks. They feed on the nectar of tubular flowers, which they pollinate. Sunbirds drink so much nectar that they need special kidneys to filter all the liquid! You can find three different types of sunbird in Cape Town:
 

• The Candelabra Flower (Brunsvigia orientalis) produces large red flower heads in late summer and early autumn. At this time of year, very few other plants are flowering in the veld. The main pollinator of this flower is the Malachite Sunbird. The flower and its pollinator are suited to each other in many ways:
  • The flower’s red colour attracts sunbirds, which can see red easily.
  • The flower is large, with a strong stem and flower stalks that act as perches for the bird.
  • The size and tubular shape of the flower matches the size and shape of the bird’s beak.
  • The flower has no smell - and most birds have no sense of smell.
  • The flower produces lots of nectar, which the birds drink.

  Question

• The common Honey Bee (Apis mellifera) pollinates many flowers. It collects both nectar and pollen, which it feeds to bee larvae in the hive.
• The Honey Bee cannot recognise red but it is attracted to yellow, blue and mauve flowers. It can also see wavelengths of light we cannot see in the ultra-violet part of the spectrum.
• The lower petals of the Blue Sage (Salvia africana-caerulea) or Brown sage (Salvia africana-lutea) form a convenient place for the bee  to land. The stamens have an unusual design: the anthers pivot like a see-saw on a short filament. When the bee crawls into the base of the flower to drink nectar, she pushes a lever and the anther swivels downwards, depositing pollen on her back. 

Try this investigation

• The Sea Rose (Orphium frutescens) grows in sand near the coast. In summer the shiny, bright pink flowers attract large Carpenter Bees (Xylocopa caffra).
• Carpenter Bees get their name from the fact that they bore holes in trees and timber and lay their eggs in chambers in the wood.
• These bees collect pollen in an unusual way called buzz pollination:
  • The bee holds onto the cluster of bright yellow, twisted anthers in the centre of the Sea Rose flower and vibrates its wings for about two seconds, producing a loud buzzing sound.
  • The buzzing causes the pollen inside the anthers to vibrate and shoot out of a pore at the tip of each anther, coating the underside of the bee.
  • When the bee visits another flower, the pollen rubs off on the stigma.
• Carpenter bees also pollinate flowers in the Pea Family but in this case they are looking for nectar, not pollen.

• Some Cape flowers attract their pollinators using oil instead of nectar as the reward. Oil-Collecting Bees (Rediviva species) have long front legs with tiny brushes on the feet to mop up oil. Scientists are doing research on these bees to find out if they feed the oil to their young or use it to waterproof their nests.
• Two examples of plants that produce oil are:
  • The Geel Gesiggie (Hemimeris racemosa): This small annual plant with yellow flowers produces oil in two hollows at the back of the flower. Several different species of Oil-Collecting Bee can pollinate the Gesiggie.
  • The Moederkappie (Pterygodium catholicum): This fairly common perennial orchid with yellow flowers has a strange scent and produces oil in a special appendage. Only one species, the Renosterveld Oil-Collecting Bee (Rediviva peringueyi) pollinates the Moederkappie.

• In addition to producing seeds (sexual reproduction) the Moederkappie also produces many underground bulbs (vegetative reproduction). It can therefore reproduce and survive for many years even if it is not pollinated.
• Another orchid known as the Babakappie (Disperis cucullata) is also only pollinated by the Renosterveld Oil-Collecting Bee (Rediviva peringueyi). This orchid does not reproduce vegetatively. It only reproduces by means of seed. If it is not pollinated, it will not produce seed and will therefore be unable to reproduce.
• Renosterveld Oil-Collecting Bees (Rediviva peringueyi) are found on the Tygerberg, but are extinct on Signal Hill. Do you think you will find the Babakappie orchid growing on Signal Hill?

• Orchids produce their pollen in tiny sacs. When a pollinator visits an orchid, it removes the entire pollen sac and takes it to another orchid to pollinate it.
• In order to stop bees visiting its flowers after they have been pollinated, the Moederkappie Orchid’s petals turn red after pollination. Bees do not notice the colour red, so they no longer notice the orchid and stop visiting it.

An endangered orchid

Look at the two similar looking Moederkappie orchids illustrated on the poster: Pterygodium catholicum is fairly common but Pterygodium cruciferum is Endangered. Can you tell the difference between them?

• Red nectar-producing flowers pollinated by sunbirds
• Yellow oil-producing flowers pollinated by oil-collecting bees.

Look for another pollination guild in the Renosterveld section of the poster. The Wine Cup (Geissorhiza radians) and the Rooibloubobbejaantjie (Babiana rubrocyanea) look very similar and both are pollinated by the same species of horsefly.

Unfortunately, female horseflies also need to suck blood to obtain the proteins they need to produce eggs. They can inflict a painful bite so look out for them if you go to see the spring flowers.

• A group of Fynbos flowers are pollinated by a weird fly with a very long tongue. The Super Long-Tongued Fly (Moegistorhynchus longirostris) has a tongue up to 8 cm long - that’s five times the length of its body!
• The fly is attracted to pale coloured flowers with red markings shown on the poster: Long-Tubed Painted Lady (Gladiolus angustus), Pypkalossie (Ixia paniculata) and Pienk Koringblom (Lapeirousia anceps). All these flowers have a long, narrow tube where the nectar is produced.
• The fly can stick its tongue down these tubes while it is flying and suck out the nectar. Fortunately, these plants flower in spring when there is relatively little wind, which makes the fly’s job easier.
• This fly is now extinct in many parts of the lowlands of Cape Town. What do you think will happen to the flowers it pollinates?

• The long-tongued fly also pollinates a rare lowland orchid called the Dragon Disa (Disa draconis).
• The orchid flowers look very much like the other flowers in the long-tongued fly’s pollination guild but they produce no nectar.
• The fly cannot tell the difference between the flowers that do produce nectar and the Disa. So it continues to pollinate the orchid, even though it gets no reward.

• The Krulletjie (Ferraria crispa) grows in rocky areas. Its flowers are brown and speckled with frilly edges. They look and smell like rotting meat.
• The flowers attract Flesh Flies (Sarcophaga haemorrhoidalis) that lay their eggs in rotting meat and faeces.
• The flies pick up bright orange pollen on their bodies as they crawl around on the flower, and find a reward of nectar at the base of the petals.
• Despite the smelly flowers, Krulletjie corms are edible.
• Another fly-pollinated plant on the poster is the White Milkwood tree (Sideroxylon inerme). It has separate male and female flowers that smell like Jeyes Fluid. Small hover flies visit the flowers and pollinate them.

The pollination of plants by animals is a good example of what ecologists call symbiosis.

A symbiotic relationship is a close relationship between two different species in which at least one of the partners benefits. There are three types of symbiosis:

• Mutualism = a close relationship in which both partners benefit
• Parasitism = a close relationship in which one partner benefits but the other is harmed
• Commensalism = a relationship in which one partner benefits but the other neither benefits nor is harmed.

• Some plants don’t need animals to help with pollination. Grasses like Rooigras (Themeda triandra) and Restios (e.g. Thamnochortus spicigerus) use the wind as their agent of pollination.
• Restios have separate male and female plants. The male flowers produce large amounts of pollen. It blows in the wind to the female flowers on another plant.
• Wind-pollinated flowers don’t need attractive petals or smells like animal-pollinated flowers do. In fact, petals would just get in the way of pollen reaching the stigma of the female flower.
• Restio flowers are brown in colour and very simple, with large anthers and feathery stigmas