Petals are the showy parts of a flower, and their main job is advertising. They draw in the bees, birds, and other animals that carry pollen from flower to flower. A petal works less like decoration and more like a sign that has to be noticed by animals that see, smell, and feel the world differently from us. The same petals can also shield a flower’s pollen from bad weather, so they serve the flower long after the first bee arrives.
Why Flowers Need Visitors at All
A flower makes seeds only after pollen reaches its female part, usually from another flower of the same kind. Plants can’t walk, so many rely on a pollinator: an animal that picks up pollen on its body while feeding and drops it on the next flower. Petals sit around the reproductive parts as the signal that food, usually nectar or pollen, is waiting.
That signal is half of a trade. The animal gets a meal as payment for its visit, and the plant gets its pollen carried to another flower, something a breeze can’t do precisely. Petals advertise the deal from a distance so visitors don’t waste trips. Because each plant is courting its own kind of customer, petals come in an enormous range of shapes and colors.
Petals are not the same thing as sepals. Sepals are usually the green, leaf-like parts that wrap the bud, while petals form the inner, usually colorful ring just inside them. In tulips and lilies the two look alike, and gardeners call them tepals. The word “petal” actually covers many showy structures that evolved separately in different plant groups, and some came from altered stamens.1Plant Ecology and Evolution. Origin and evolution of petals in angiosperms
Color and Hidden Ultraviolet Patterns
Different petal pigments produce different color signals to bees, flies, butterflies, and birds.2Frontiers in Ecology and Evolution. Major Flower Pigments Originate Different Colour Signals to Pollinators Certain yellow pigments stood out most to all these pollinators, with the more common yellows and oranges next.3Frontiers in Ecology and Evolution. Major Flower Pigments Originate Different Colour Signals to Pollinators The red-to-purple pigments found in most flowers gave some of the weakest color contrast.4Frontiers in Ecology and Evolution. Major Flower Pigments Originate Different Colour Signals to Pollinators White flowers, which carry ultraviolet-absorbing pigments, gave bees the strongest light-versus-dark contrast.5Frontiers in Ecology and Evolution. Major Flower Pigments Originate Different Colour Signals to Pollinators
Bees and humans see flowers differently. Bees detect ultraviolet light that our eyes can’t, and they see red poorly, so a plain red petal may look dull to them. A flower that looks plain to us can carry bold patterns in a bee’s view. Photos taken with ultraviolet cameras reveal these hidden markings.
Red flowers show how this can favor one visitor over another. Many red, bird-pollinated flowers in California look barely distinct to bees.6PubMed. UV pigments of red bird-pollinated flowers attract birds and deter bees To hummingbird eyes, the same flowers stood out about 1.5 times more than bee-pollinated flowers.7PubMed. UV pigments of red bird-pollinated flowers attract birds and deter bees The reason is pigment: bird-pollinated red flowers held about 5 times more ultraviolet-absorbing pigment than red bee flowers.8PubMed. UV pigments of red bird-pollinated flowers attract birds and deter bees One pigment can attract the visitor the plant wants and discourage a less useful one.
Markings on petals work as signposts. Lines and spots on petals, often called nectar guides, point visitors toward the nectar, and in one tested flower they clearly worked and helped seed production.9PubMed Central. Floral signposts: testing the significance of visual ‘nectar guides’ for pollinator behaviour and plant fitness Many flowers also have an ultraviolet bullseye, a dark center we can’t see but bees can. In a field test, though, the bullseye mainly helped visitors spot flowers from a distance, not find the center once landed.10Functional Ecology. Dissecting pollinator responses to a ubiquitous ultraviolet floral pattern in the wild In hotter, sunnier, drier places, some flowers grow larger ultraviolet patterns and more red-to-purple pigment.11PubMed Central. Climate Predicts UV Floral Pattern Size, Anthocyanin Concentration, and Pollen Performance in Clarkia unguiculata
You can look for nectar guides in your own garden. Foxgloves, pansies, and irises have streaks leading inward, and the lines usually converge on the opening where nectar sits. Watch a bee land and you can see it follow them to the center.
Scent, Texture, and Electric Signals
Petals are generally the main source of a flower’s fragrance, though other flower parts sometimes add to it.12PubMed Central. Volatile Organic Compounds Emitted by Flowers: Ecological Roles, Production by Plants, Extraction, and Identification Scent is made in special cells on the petal surface, some of them cone-shaped.13PubMed Central. Volatile Organic Compounds Emitted by Flowers: Ecological Roles, Production by Plants, Extraction, and Identification Scent carries over distance and in darkness, where color fades, so it can draw pollinators from out of sight, which is why moth flowers are often pale and strongly scented at dusk.
Most petals are covered in tiny cone-shaped cells.14PubMed. Conical epidermal cells allow bees to grip flowers and increase foraging efficiency These cells give grip on what would otherwise be a slippery surface.15Annals of Botany. Why do so many petals have conical epidermal cells? Bumblebees can tell cone-celled petals from flat ones by touch alone, and they prefer cone-celled flowers more strongly when the flower is steep or hard to hold.16Annals of Botany. Why do so many petals have conical epidermal cells? Good grip lets bees feed faster.17PubMed. Conical epidermal cells allow bees to grip flowers and increase foraging efficiency
You can feel this yourself. Many petals feel velvety because of their cone-shaped cells, and that is the same texture a bee’s feet grip. Smooth, glossy petals like buttercups have flatter cells.
Flowers also carry small electric fields that bumblebees can detect and tell apart.18PubMed. Detection and learning of floral electric fields by bumblebees Because bees carry their own charge, a visit changes the flower’s field within seconds.19PubMed. Detection and learning of floral electric fields by bumblebees Electric cues may help bees remember which flowers paid off, and may signal that a flower was just emptied.
Petals as Landing Pads and Gatekeepers
Petal shape can decide who gets in. In pea-family flowers, an insect lands on the side petals and pushes down on the lower petals to reach nectar.20PubMed Central. Synergistic Effects of Flower Color and Mechanical Barriers on Pollinator Selection Within the Papilionoideae of Fabaceae That push takes enough body weight and strength, so small, weak insects can’t open the flower.21PubMed Central. Synergistic Effects of Flower Color and Mechanical Barriers on Pollinator Selection Within the Papilionoideae of Fabaceae As the flower opens, pollen brushes onto the insect’s body.22PubMed Central. Synergistic Effects of Flower Color and Mechanical Barriers on Pollinator Selection Within the Papilionoideae of Fabaceae
With a bumblebee, the side petals serve as a perch. Its weight presses the lower petals down, and hidden pollen and stigma pop up against its belly. When it leaves, the petals spring back for the next visitor.
In columbines, the shape and color of long petal spurs are matched to different pollinators.23PubMed Central. Aquilegia as a model system for the evolution and ecology of petals Nectar pools at the spur tip, reachable only by long tongues or beaks. Hummingbirds and moths can get it, short-tongued bees cannot, and that keeps the nectar for visitors most likely to carry pollen onward.
Protecting Pollen and Keeping Warm
Pollen of many flowers is damaged by water.24PubMed Central. Pollen resistance to water in 80 angiosperm species: flower structures protect rain-susceptible pollen Flowers whose structures fully cover their pollen tended to have rain-sensitive pollen, while flowers with exposed pollen more often had water-resistant pollen.25PubMed Central. Pollen resistance to water in 80 angiosperm species: flower structures protect rain-susceptible pollen
Some petals handle water directly. Pansy petals carry tall pointed bumps with fine folds that make water bead up and roll off, which keeps the surface clean while insects can still grip it. Rose petals are water-repellent but hold droplets in place, so they avoid getting waterlogged.
Many flowers close their petals at night.26Flora: Morphology, Distribution, Functional Ecology of Plants. A new pollination system in non-cleistogamous species of Viola results from nyctinastic (night-closing) petal movements – A mixed outcrossing-selfing strategy Closing may reduce frost risk, save scent and energy for daytime pollinators, and keep pollen dry from rain and dew.27Flora: Morphology, Distribution, Functional Ecology of Plants. A new pollination system in non-cleistogamous species of Viola results from nyctinastic (night-closing) petal movements – A mixed outcrossing-selfing strategy When crocus flowers were prevented from closing, their pollen became less viable.28Flora: Morphology, Distribution, Functional Ecology of Plants. Flower closure enhances pollen viability in Crocus discolor G. Reuss
You can watch this happen. Crocuses and tulips often close on cloudy or cold days and reopen when sunshine returns, sometimes within an hour. Daisies and some poppies also fold up at dusk. In these flowers, the movement responds mainly to light and temperature, not touch.
Some petals act as heat traps. In mountain flowers, petals cupped when cold and flattened when warm.29PubMed. Behavioural Thermoregulation of Flowers via Petal Movement Cupping focuses sunlight into the flower’s center, and a 20-degree change in petal angle warmed the flower by about 0.46°C.30PubMed. Behavioural Thermoregulation of Flowers via Petal Movement A warmer center may help pollen and attract cold insects that bask.
What Happens to Petals After Pollination
In the species studied, pollination triggers the plant hormone ethylene, which reduces the flower’s attractiveness and shortens its life.31Journal of Experimental Botany. Effects of pollination on floral attraction and longevity Once it builds up, ethylene speeds the changes that make petals lose their appeal, so they may wilt, fade, or drop soon after successful pollination.32Journal of Experimental Botany. Effects of pollination on floral attraction and longevity The plant stops spending energy on advertising and redirects it to seeds.
The same hormone explains why cut flowers fade near fruit. Ripening fruit like bananas and apples releases ethylene, so keeping a bouquet away from a fruit bowl can make it last longer. Florists sell treatments that block ethylene for this reason.
Some flowers change color after pollination rather than dropping petals. This steers pollinators to unvisited flowers on the same plant, so visitors save time and the plant gets more flowers pollinated.
Can Petals Make Their Own Food
Green petals, like those of green chrysanthemums, contain the same light-capturing parts as leaves.33PubMed Central. Mechanisms underlying green flower formation These parts are what let leaves turn sunlight into sugar, so green petals have the machinery to do some of the same work. Having it doesn’t mean the petal makes enough food to support itself, and the result depends on how much light the petal gets and how well the tissue is built for it.
In one gardenia, flower buds photosynthesize and store carbon needed for later blooming.34bioRxiv. Petal photosynthesis and dynamic alterations of carbon metabolism orchestrate floral maturation in Gardenia carinata But green orchid petals lost sugar when leaves were shaded, showing they mostly rely on leaves.35PubMed Central. Mechanisms underlying green flower formation Young green petals photosynthesize more than aging ones.36PubMed Central. Mechanisms underlying green flower formation
Most petals aren’t green because green blends into leaves and is hard for pollinators to spot. Color pigments replace chlorophyll in most petals, and green-flowered garden varieties often owe their color to breeding.
Flowers With Few or No Petals
Wind-pollinated flowers have reduced petals, are usually small and inconspicuous, and typically make little or no nectar or scent.37International Review of Cytology. Wind Pollination Mechanisms and Aerobiology Grasses, oaks, and many trees bloom without anyone noticing. Petals cost the plant energy, so they are kept mainly where animals do the carrying.
Sometimes the showy part isn’t a petal at all. In poinsettias the red parts are leaves called bracts, and in dogwoods the white “petals” are bracts too. These plants advertise with other parts while their true petals stay small.
Double Flowers and Garden Bees
Double flowers have extra petals where pollen-making and seed-making parts would be, and they are often partly or fully sterile.38UW News. Gardener’s delight offers glimpse into the evolution of flowering plants The extra petals take the place of those parts, so the flower trades usefulness for looks. In roses, a change in where one gene is active turns stamens into petals,39PubMed Central. Tinkering with the C-Function: A Molecular Frame for the Selection of Double Flowers in Cultivated Roses and breeders selected this change repeatedly to create showy roses.40PubMed Central. Tinkering with the C-Function: A Molecular Frame for the Selection of Double Flowers in Cultivated Roses
If you want to help bees, single-flowered varieties show an open center with visible pollen. Dense double blooms can block bees from reaching any nectar. Check plant labels for “single,” or look for a visible center, and mix single forms into your garden to support local pollinators.