THE INTIMATE
WORLD OF
FLOWERS
Welcome to the secret world of flowers!
All these striking flowers with intense colours, amazing forms and wonderful scents. What is their purpose? Are they here for our pleasure? Just like animals, plants need to �mate� or reproduce in order for life to continue. Reproduction in plants takes place in the flowers, right before our eyes, and is called pollination. In other words, plants make flowers for their own benefit. In this pamphlet you can read fascinating descriptions about the pollination of plants and the help they get from the wind and insects to ensure successful reproduction.
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Indicators in the text and signs in the gardens Plants whose pollination is described in more detail are marked with the common blue butterfly, both in the text and the flower beds, making them easy to spot. The plants have been chosen so that each example of pollination can be seen on some flowering plant regardless of when you visit during the season. Sp, Su, A. These letters are placed after the species name and indicate the time of the year when the plant flowers. Sp = Spring Su = Summer A = Autumn 4.2.C - Figures and characters placed after the plant name in the text, refer to the garden beds in the Systematic Garden at Fredriksdal. Finally, there is a map showing the location of the beds in the gardens. Flora’s Temple is situated in the heart of the Systematic Garden. Here you can find more information about the Botanical Gardens at Fredriksdal, where the natural flora of the region Sküne is displayed.
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contentS Plants as sexual beings sid 6 Flowers need “a helping hand� in the sexual act
sid 7
Butterflies as pollination aids sid 9 Butterflies sid 10 Moths sid 13 Hymenopterans (bees, bumblebees and wasps) as pollination aids sid 14 Beetles as pollination aids sid 21 Flies and mosquitoes as pollination aids sid 22 The wind and insects work for free in the service of humans
sid 24
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Plants as sexual beings
Plants generally have open flowers, where male and female reproductive organs can be easily viewed. Most plants are hermaphrodites and have both male and female reproductive organs on one and the same flower. The male reproductive organs, called stamens, are topped by anthers bearing pollen. The female reproductive organ, the pistil, comprises the ovary, style and stigma.
Plants with clearly visible reproductive organs Lily-of-the-valley (Sp) – Covallaria majalis 5.3.B Crane’s-bill (Su) – Geranium sp. 3.1.B Suffolk lungwort (Sp) – Pulmonaria obscura 2.1.B Bluebells (Su) – Campanula sp. 1.4.C Wood sorrel (Sp) – Oxalis acetosella 3.2.B Mullein (Su, A) – Verbascum sp. 1.3.C.
Pollination involves the transfer of pollen from the stamen to the stigma of the pistil. This normally takes place within one and the same species, but between one individual and another. Fertilisation occurs when the male nucleus of the pollen grain fuses with the egg cell (ovum) in the ovary of the pistil. After some time fruits are formed, containing seeds which are the offspring of the plant. More information about this process can be found at Freja Frö, an exhibition with wood sculptures in the Systematic Garden at Fredriksdal. Linnaeus was the first to consider plants as sexual beings. He compared the structure of flowers to human relationships when he placed plants in classes and orders according to the number of stamens and pistils they had. It was often a matter of one woman (the pistil) living in a relationship with many men (the stamens). In the Systematic Garden, there is a specific garden bed where plants are displayed according to Linnaeus’s sexual system.
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Pollination
Stigma
Stamen
Ovary
Style
Flowers need “a helping hand” in the sexual act
How is pollen transferred from the stamen to the pistil? Flowers seldom manage to reproduce on their own accord, but require help during the sexual act. In order for the offspring to obtain as wide a genetic variation as possible, pollen should preferably be transferred from one plant to another within the same species. Some plants make use of the wind. Relying on the wind to transport pollen grains is somewhat risky since “the wind blows wherever it pleases”. Plants pollinated by wind, therefore, produce an enormous amount of pollen. This applies to many of our trees, which facilitate pollination by flowering early in the spring before they put out leaves. The pollen grains are then easily dispersed through the air without leaves to obstruct their passage. The great quantities of pollen often cause people to develop allergies to, for instance, hazel, alder, elm and birch. Grasses (Sp, Su) – Poaceae 5.1.B and Mugwort (Su, A) – Artemisia vulgaris 1.2.C, are other examples of allergy-inducing plants pollinated by wind. The stamens often hang far out of the flowers on slender filaments, so that the pollen is easily caught by the wind. In other words, it is vast quantities of male gametes (sperm cells) that cause the problems in people’s respiratory passages. Has anyone ever thought about that? These gametes have ended up in the wrong place altogether, where they have no use and just cause problems.
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The stamens on grass inflorescences dangle on long filaments to enable the wind to catch the pollen grains
A more reliable way for plants to be pollinated is by employing insects to transfer the pollen from one flower to another when it clings to their bodies. The insects do not actively take part in the sexual act, but find themselves in the flower in search of food. Offering insects something edible is one way for plants to ensure pollination. The food consists of protein-rich pollen and nectar containing carbohydrates in the form of sugars. In order for insects to find their way to the food, plants have developed big, eyecatching flowers with beautiful colours, exciting shapes and wonderful scents. Insects see the world differently to us. They have the ability to detect ultraviolet light and can therefore see patterns in the flowers where the human eye cannot. Most of the scents are there so that the insects will remember them and associate them with food. In some cases flowers attract insects through the use of scents that resemble something else that the insect might be looking for, such as rotten meat or amorous females ready to mate. Plants and insects have developed and adapted to each other over millions of years. However, some flowers are not particularly specialised. They are open with nectar that is fairly accessible for visitors, can be pollinated by widely diverse groups of insects, and generally offer pollen as the reward. In other cases, flowers are pollinated by specific insects. The reward for these insects is often nectar, well hidden deep within the flower.
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Some plants are able to self-pollinate, where pollination takes place within one and the same flower. Self-pollinating plants often have small, insignificant flowers that lack scent and do not produce nectar or pollen in any great amount. The advantage of this method is that offspring are guaranteed without the investment of extra resources, but at the cost of genetic variation. Should the environment change in any way, these plants have a poor ability to adapt to the new environment since all plants within the species are similar. Many self-pollinating plants are annuals and can quickly colonise bare earth.
Plants with self-pollinating flowers Chickweed (Sp, Su, A) – Stellaria media 4.2.C Smooth rupturewort (Su) – Herniaria glabra 4.2.B
Butterflies as pollination aids
Butterflies as a group are divided into butterflies and moths, and the flowers that they visit differ in form and scent. Butterflies do not gather food for their offspring, but consume all nourishment themselves. They sip nectar with the help of a proboscis, a long tubular sucking organ that is rolled up under the head when not in use. A flower typically visited by butterflies has nectar stored deep within a floral tube or spur. Butterflies can exploit many different types of flowers, but certain flowers are pollinated only by butterflies. A flower typically visited by moths
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Butterflies
Flowers pollinated by butterflies often have weak scents and reddish colours. Butterflies are, in fact, the only insects able to see red hues. The flowers are often upright with a flat top that functions as a landing site. This is necessary since butterflies are stationary while feeding on nectar. Many flowers have such long floral spurs that only the long proboscis of a butterfly can reach the nectar. The plant clearly marks the path to the nectar with dots, lines or furrows on the petals of the flower. Red campion (Sp) – Silene dioica 4.2.C. Red campion has unisexual flowers on separate male and female plants (dioecious). Some plants have flowers bearing only stamens, others only pistils. The female flowers differ from the male flowers in that they have a swollen calyx containing the ovary where the seeds are formed. Most animals have separate sexes, but among plants this is unusual. A design with separate male and female plants prevents self-pollination. Red campion
Female plant with swollen calyx containing the ovary.
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Male plant
Cowslip (Sp) – Primula veris 2.4.D Cowslip is pollinated by butterflies with long proboscides, able to reach the nectar stored deep within the flower. This plant bears two types of flowers: the style is long and the stamens short on the one, and vice versa on the other. An insect visiting a flower with a short style will collect pollen from the long stamens. When the insect then visits a flower with a long style, the stigma is placed at the right height to enable pollen from the previous flower to be rubbed off onto it. At the same time the butterfly is powdered with pollen from the short stamens, which can then be transferred to flowers with short styles. Also have a look at Cowslip, Bird’s-eye primrose, and Primrose in the garden beds. They too have flowers constructed this way. Primrose
Flower with short style
Flower with long style
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Forget-me-not (Sp, Su) – Myosotis sp 2.2.B There are several different species of Forget-me-not. All of them have lovely, sky-blue flowers. The flower is flat and functions as a landing site for butterflies that wish to sip nectar from deep within the flower. Showing the way is a wreath of yellow or white hairs in the centre of the flower, forming a ring around the entrance to the floral tube. This also functions as a water-repellent cover over the anthers. In this way the entrance is partly covered, making it possible only for butterflies with long proboscides to reach the nectar. Pollen clings to them while they sip nectar and can thus be transferred onto the next flower. Forget-me-not with a wreath of hair in the centre of the flower showing the way to the nectar.
Examples of other flowers pollinated by butterflies Ragged-robin (Sp, Su) – Lychnis flos-cuculi 4.2.C Maiden pink (Su) – Dianthus deltoides 4.2.C Corncockle (Su) – Agrostemma githago 4.2.C Bloody crane’s-bill (Su) – Geranium sanguineum 3.1.B
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Moths
Flowers typically visited by moths are open at night. They are often pale in colour or completely white, and their scent is strongest during dusk and dawn, and at night. Moths have a well-developed sense of smell located on their antennae. They hover in mid air - especially hawk moths - while feeding on nectar, often located deep within the flower in floral tubes or spurs. These flowers, therefore, do not need a landing site. Honeysuckle (Su) – Lonicera periclymenum 1.4.A Honeysuckle only starts spreading its scent in the evening, when moths become active. The flower has a fairly slender, deep floral tube. The nectar available at its base can only be reached by large moths with very long proboscides.
Examples of other plants pollinated by moths Lily-of-the-valley (Sp) – Covallaria majalis 5.3.B Nottingham catchfly (Su, A) – Silene nutans 4.2.C Suffolk lungwort (Sp) – Pulmonaria obscura 2.1.B Evening-primrose (Su, A) – Oenothera biennis 2.3.C Valerian (Su) – Valeriana officinalis 1.4.B White campion (Su, A) – Silene latifolia 4.2.C Soapwort (Su, A) – Saponaria officinalis 4.2.C
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Hymenopterans (bees, bumblebees and wasps) as pollination aids
Hymenopterans pollinate more kinds of flowers than all the other insect groups put together. Pollen clings easily to their hairy bodies. Hymenopterans prefer flowers with yellow and blue colours and are able to open up flowers that are closed. They often find nectar with the help of streaks and spots. Their mouthparts are shorter than those of butterflies, and many of them have flat tongues, meaning that they can only lap nectar, not suck it up. Bees and bumblebees are important pollinators of the large flowering plants within the following plant families: the mint family – Lamiaceae 2.1.B, 2.1.C, the legume family – Fabaceae 3.2.B, 3.2.C, 3.2.D, 3.4.C, 3.4.C, and the figwort family – Scrophulariaceae 1.3.B, 1.3.C. From an economical perspective, bees and bumblebees are the most important pollinators in that they pollinate fruit trees and berry bushes. Their significance lies in the fact that they do not only gather nectar and pollen for themselves, but also for their larvae, meaning that they must visit a great number of flowers. Bees are best at remembering flower shapes. They are also able to inform one another of good sites for food collection and areas with good flower populations. Wasps are chiefly predators and feed their larvae mostly on animal matter. They do, however, visit flowers, especially at the end of the growth season in search of energyrich nectar. Flower typically pollinated by bumblebees and bees.
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Foxgloves (Su, A) – Digitalis purpurea 1.3.C Foxgloves are specially designed to suit bumblebees. Speckles on the fused petals, called a corolla tube, show the way to the nectar inside the flower. When the bumblebee crawls into the flower, pollen is gathered on its back. Bees are not able to enter the flower because they use their wings to propel themselves forward, and the cramped space of the corolla tube prevents this. Foxgloves have a long flowering season and individual flowers in the inflorescence open from the bottom up. In each flower the stamens develop before the pistil. This is well adapted to the behaviour of bumblebees, since they always start at the bottom of the inflorescence and make their way upwards. This reduces the risk of the flower self-pollinating. Bumblebees have good memories; they can remember flower shapes and good collecting sites for several days, ensuring pollination of the flowers. Foxglove
Young plant Mature plant
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Foxglove Upper section of the flower removed.
The flower in the male phase.
The flower in the female phase.
Common toadflax (Su, A) – Linaria vulgaris 1.3.C Toadflax has a flower that is specialised for pollination by bees and bumblebees. The flower is closed and can only be opened by insects with great strength. The nectar is contained at the bottom of a long, narrow floral tube, and only certain species of bumblebees and bees have sufficiently long proboscides to reach it. A kink on the lower lip of the flower has a darker yellow colour than the rest of the flower and functions as a guide to the location of the nectar. Common bird’s-foot trefoil (Su) – Lotus corniculatus 3.2.D All the flowers of leguminous plants have a specific structure. They consist of four different parts: a standard petal (vexillum), two wing petals and a keel petal. The standard bears the markings that show the insect where to land. In the bird’s-foot trefoil the wings curve over the keel like a saddle and when an insect that is heavy enough lands on the wings, both the wings and the keel are depressed. The pressure causes a ribbon of pollen to be squeezed from an opening at the tip of the keel and to attach to the underside of the insect’s body. After some time the pistil matures and the stigma pushes through the tip of the keel, where it can receive pollen from visits made to other flowers. 16
Leguminous flower with standard, wings and keel.
Standard
Wing
Wing
Keel Common bird’s-foot trefoil. Longitudinal section through the keel.
In a state of rest.
After the keel has been depressed and the pollen squeezed out.
The pistil has pushed its way out.
Example of another leguminous plant that is pollinated in a similar way Field restharrow (Su, A) – Ononis spinosa ssp. arvensis 3.2.B
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Western marsh-orchid (Sp) – Dactylorhiza majalis 4.3.A, 4.4.A Marsh-orchids, like all other orchids in Sweden, are protected by law. The lower petal functions as a landing site for, primarily, bees and bumblebees. The impact of colour is amplified by the large number of flowers gathered together on one inflorescence. The pattern of spots on the landing site leads to the centre of the flower. Once there, the insect triggers a mechanism causing the single stamen to release the two pollinia, each a waxy mass of pollen grains. Each pollinium has a sticky adhesive pad (viscidium), which adheres to the insect’s head. The two pollinia stand erect at first, like two horns on the insect, but within the course of half a minute they bend 90 degrees so that they point forwards instead. When the insect visits the next flower, the pollinia are positioned in a way that enables them to make contact with the stigma. Bee with pollinium attached to its head. Pollinium
Pollinium
At the moment of adherence.
30 seconds later.
Fly orchid (Sp) – Ophrys insectifera 4.3.A, 4.4.A This orchid has flowers that look and smell like female members of the Sphecidae wasps who are ready to mate. The likeness is so great that males land on the flowers in the belief that they are female wasps. The flower has hairs that correspond to those of a female wasp, making it possible for the male to orientate himself correctly on the flower and carry out the motions of mating. At the same time the pollinia adhere to the insect and are carried along to the next flower. Broad-leaved helleborine (Su) – Epipactis helleborine 4.3.A, 4.4.A Broad-leaved helleborine is an orchid primarily pollinated by wasps, but bees and bumblebees are also frequent visitors to the flowers. The lower lip (labellum) of the flower functions as a landing site and while sitting there the insect can feed on the rich nectar, 18
collected in a cup (hypochile) further in on the lip. Located above the nectar cup are the stigma and the two pollinia. While a wasp feeds on the nectar, the sticky adhesive pads of the pollinia adhere to the insect’s face - on the antennae, mouthparts or eyes. The nectar is toxic and the soon intoxicated insect becomes unable to remove the pollinia from its face. The wasp’s ability to fly is reduced and it therefore stays longer on the same inflorescence, crawling from flower to flower. Pollination increases as a result. The wasps become addicted to the toxic liquid and return readily to new flowers of helleborine in the days that follow. Purple loosestrife (Su, A) – Lythrum salicaria 2.3.C Purple loosestrife is usually pollinated by bumblebees and bees, but also by other insects. Like primroses, its stamens and pistils come in different lengths on different flowers in order to encourage cross-pollination. But here the flowers are even more refined. There are three different kinds of flowers and three different lengths of stamens and pistils, distributed in different ways in each of the three types of flower. Pollination only takes place between stamens and pistils of the same length. Purple loosestrife Medium length style
Long style
Short style
Notice the three different lengths of the stamens and pistils. The arrows demonstrate possible pollen transfer. Oxeye daisy (Su) – Leucanthemum vulgare 1.2.C The oxeye daisy attempts to deceive insects into seeing it as a single large flower, but in reality it comprises many small flowers collected into a disc-shaped inflorescence. Each disc attracts bees, bumblebees and hoverflies, but even butterflies and beetles pollinate these flowers. The chief purpose of the petal-like ray florets is for display. In some cases they are completely sterile, in other cases they bear only pistils. The tubular flowers or 19
disc florets in the centre of the inflorescence are bisexual. The stamens form a fused tube around the style. The stamens mature before the pistil, already when the flower is still in bud form. After that the style shoots up through the stamen tube. This reduces the risk of self-pollination. The nectar is located further down in the tubular corolla and is easily reached by insects. Oxeye daisy
Composite flower head
Bisexual tubular disc floret with stamens and pistil.
Female ray floret with pistil.
Many others plants in the composite flower family have the same flower structure and are pollinated in similar ways Common daisy (Sp, Su, A) – Bellis perennis 1.1.B Scentless mayweed (Su, A) – Tripleurospermum perforatum 1.2.C Mountain arnica (Su) – Arnica montana 1.2.B Yellow chamomile (Su, A) – Anthemis tinctoria 1.2.C Common ragwort (Su, A) – Senecio jacobaea 1.2.B
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Beetles as pollination aids
Beetles are clumsy insects. Flowers suitable for pollination by beetles must therefore have a big enough surface for the beetles to land on, such as members of the umbelliferous family – Apiaceae 2.3.B, 2.4.B, 2.4.A and the buttercup family – Ranuncualceae 4.1.B. Beetles are attracted more by scent than by form and colour. Their mouthparts are short and best adapted for chewing, and they readily eat pollen. If they feed on nectar it must be within easy reach in flat, open flowers. The flowers visited by beetles can also be pollinated by a number of other insects. It is rare to find flowers that are specialised for pollination by beetles. Flower typically pollinated by beetles
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Flies and mosquitoes as pollination aids
Flies visit simply designed flowers that are open and flat, with nectar and pollen within easy reach. The flowers are often white, yellow, or greenish in colour and they often emit unpleasant odours. Larger flies and mosquitoes have relatively long proboscides with which they can suck nectar from tubular flowers. Some flies and mosquitoes are attracted to flowers that smell like carrion or urine when they are in search of suitable places to lay their eggs. Wild chervil (Sp) – Anthriscus sylvestris 2.3.B and other umbelliferous flowers Members belonging to the family of umbelliferous plants have flowers that are clustered into umbrella-like inflorescences. This mass effect makes it easier for insects to find them. The flowers are flat and open, and the nectar is easily accessible. Hoverflies and other flies with short proboscides often pollinate this plant family; approaching the flowers can set off a whole cloud of flies. Hoverflies resemble bees and wasps, but their pattern of movement is different and they can hover in the same spot for long periods. Lords-and-Ladies (Sp) – Arum maculatum 5.1.C Moth flies are attracted by the stench of urine emitted by the spadix and land on the inside of the white leaf-like spathe. They lose their grip and slide into the floral chamber in the interior of the flower. If the moth flies are carrying pollen from previous visits to other flowers, the female flowers at the base of the spadix will be pollinated. The moth flies are unable to escape since the wall of the floral chamber is smooth and slippery, and the opening is blocked by hairs. The male flowers, positioned above the female flowers on the spadix, mature after a day. The hairs wither and the surface of the chamber wall becomes rough, enabling the moth flies to make their way out, their bodies loaded with pollen. Then, hopefully, a new stench of urine attracts them again and the whole story repeats itself. The odour lures the moth flies into thinking they have found cow manure in which to lay their eggs. 22
Lords-and-ladies
Hairs
Male flowers
Female flowers
Birthwort (Su) – Aristolochia clematitis 4.4.B Like that of Lords-and-ladies, this flower is also designed as a trap for insects. The flies are lead down a tube to the nectar at the base of the flower. If the flies are carrying pollen, the pistils get pollinated at the same time. Hairs pointing downwards prevent the insect from getting out. After pollination the hairs wither, the male flowers mature and new pollen clings to the fly on its way out. Birthwort
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The wind and insects work for free in the service of humans
Linnaeus was the first to understand the significance of the role played by insects in the balance existing between different plant and animal groups. According to him, no other animal group is more crucial to maintaining this balance than insects. The wind and insects aid pollination by transferring the pollen from one flower to another. They are essential to the world economy because they pollinate plants of great value to people. The wind is important, for instance, for maize and all other crops cultivated for the production of cereal grains. Insects assist us in vegetable cultivation which produces matured fruits like tomatoes and cucumbers, but also in all fruit farming. Without their help there would be no apples, cherries, oranges, almonds or currants. These insects provide us with invaluable, free services and we should do everything within our power to make sure that they thrive in nature and in our gardens. In recent years the decline of many insect populations has attracted much attention. For centuries, the diversity of small habitats created by traditional farming methods has resulted in favourable conditions for insects as a group. The shift to more efficient cultivation systems and large-scale production has had a serious impact on the number of insects. Edge habitats have disappeared, inorganic fertilisers have reduced diversity and hayfields and pastures rich in floral diversity have been converted into commercially managed fields and forests. Fredriksdal’s fields and pastures are managed using traditional farming methods. No pesticides or inorganic fertilisers are used and the fields are cut annually using scythes or sickle mowers. There is a great biological diversity to be found here in terms of herbs, grasses, fungi and insects. In the Systematic Garden at Fredriksdal there is an Insect Hotel that serves as a shelter for many pollinating insects. Predatory insects that prey on undesirable insects in our gardens and other cultivations, can also find shelter in our hotel. By planting nectar-producing plants in your garden, you will help to ensure that many different insects are able to survive and continue pollinating our gardens.
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1.1.C 1.1.B
1.2.C 1.2.B
1.1.A
1.2.A
1.3.A
1.4.A
1.3.B 1.3.C
2.1.C
1.4.B 1.4.C
2.2.C
2.1.B
2.2.B
2.1.A
2.2.A
2.3.A
2.4.A
2.3.B 2.3.C
3.1.C
2.4.D
2.4.B 2.4.C
3.2.C
3.1.B 3.1.A
3.2.A
3.3.A
3.4.A
3.3.B 3.3.C
4.1.C
6.1.B
6.2.A
6.2.B
6.1.C
6.1.D
6.2.C
6.2.D
6.3.A
6.3.B
6.4.A
6.4.B
6.3.C
6.3.D
6.4.C
6.4.D
3.2.D
3.4.B 3.4.C
4.2.C
4.1.B
6.1.A
3.2.B
4.2.B
5.1.C
5.2.C
5.1.B
5.2.B
4.1.A
4.2.A
5.1.A
5.2.A
4.3.A
4.4.A
5.3.A
5.4.A
4.3.B 4.3.C
4.4.B 4.4.C
5.3.B 5.3.C
5.4.B 5.4.C
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Text: Karin Hjelmér Illustrations: Liselotte Nilsson, Marie Widén Fact checking: Lars Pettersson, researcher at the Department of Biology, Lund University Layout: Caroline Flindt Translation into English: Gayle Rolando A big thank you goes to the students of the Individual Programme at the school Nicolaiskolan, in Helsingborg, for their work in creating the wire art butterflies. With financial support from Hervid Vallin’s Memorial Fund.
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