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Petal

life science Maturity 13-18 Next article →

Petals are modified leaves that serve as a vital part of a flower's reproductive system. They form an inner whorl of tissue that surrounds the reproductive organs. Collectively, all the petals in a single flower are known as the corolla.

Mature flower diagram
Mature flower diagram

The corolla is part of the perianth, which is the non-reproductive portion of the flower. This perianth also includes the calyx, which is the outer whorl made of sepals.

Perianth morphology fusion aposepalous apopetalous
Perianth morphology fusion aposepalous apopetalous

In some plant groups, the sepals and petals are difficult to tell apart. These undifferentiated parts are called tepals.

20140226Narcissus2
20140226Narcissus2

Plants like tulips or those in the Aloe genus use these tepals. If these tepals look like colorful petals, they are described as petaloid.

Scientists study how petals are structured to understand plant evolution. Charles Darwin famously studied the origins of elongated corollae and long corolla tubes. The way petals are joined or separate is a key way to classify them. If the petals are entirely separate from one another, the corolla is called apopetalous. This is also known as being polypetalous or choripetalous.

Perianth morphology fusion aposepalous apopetalous
Perianth morphology fusion aposepalous apopetalous

If the petals are at least partially fused together, the flower is gamopetalous or sympetalous. When tepals are fused, the term syntepalous is used. Fused petals often grow into a long structure called a corolla tube.

2007 brugmansia aurea
2007 brugmansia aurea

This structure can change how pollinators interact with the flower.

Petals also show different types of symmetry. Some flowers are actinomorphic, which means they are radially symmetrical. In these flowers, all petals are essentially identical in size and shape.

Geranium incanum 9156s
Geranium incanum 9156s

Other flowers are zygomorphic, meaning they have bilateral symmetry. These flowers can only be divided into two equal halves along one single plane.

White pea flower
White pea flower

Zygomorphic flowers are common in the pea family and in orchids. This shape often helps guide specific animals to the center of the flower. In some cases, the petals are even modified to form a floral cup, or hypanthium.

20140226Narcissus2
20140226Narcissus2

This cup sits above the ovary and supports the petals.

Individual petals can be divided into two distinct anatomical parts. The upper, broader part is called the blade, which is similar to a leaf blade. The lower, narrower part is called the claw, which resembles a leaf petiole.

These two parts are separated by a region called the limb. In certain families like Brassicaceae, these claws are very well developed. The number of petals can also help scientists classify plants. For example, eudicots frequently have four or five petals. Monocots often have three or six petals, though there are many exceptions.

20140226Narcissus2
20140226Narcissus2

The formation of petals is explained by the ABC model of flower development. This genetic model suggests that sepals, petals, stamens, and carpels are all modified versions of each other. Research suggests that the specific mechanisms to form petals likely evolved very few times. It may have happened only once rather than evolving repeatedly from stamens. This shows how deeply the structure of a petal is tied to the plant's genetic history. The diversity of petal shapes and colors is a result of these evolutionary paths.

Petals play a massive role in the process of pollination. Pollination is necessary for the sexual reproduction of higher plants. Since pollen cannot move on its own, it requires wind or animals to carry it to a stigma. Petals act as an incentive to attract these pollinators. Wind-pollinated species, like grasses, often have very small petals or are apetalous.

White pea flower
White pea flower

They do not need to attract animals, so they produce large amounts of pollen instead. In contrast, animal-pollinated flowers use color and scent to compete for visitors.

Different animals require different petal strategies. Insects like bees and butterflies are attracted to colors and scents. Some flowers have nectar guides, which are patterns that lead insects to food.

White pea flower
White pea flower

Many of these guides are visible in ultraviolet light, which humans cannot see. Other flowers use scent, like the sweet smell of a rose. Some even mimic the smell of rotting meat to attract flies. Birds are attracted to large, bright colors. The tree fuchsia can even change from green to red to communicate with birds.

Even bats are attracted to specific flowers. The Dactylanthus taylorii uses a strong scent and nectar to attract short-tailed bats.

20140226Narcissus2
20140226Narcissus2
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🖼️ Images & Media (8)
File:Mature flower diagram.svg
Mature flower diagram.svg
File:Perianth morphology fusion aposepalous apopetalous.png
Perianth morphology fusion aposepalous...
File:2007 brugmansia aurea.jpg
2007 brugmansia aurea.jpg
File:Pelargonium peltatum 9245s.jpg
Pelargonium peltatum 9245s.jpg
File:Geranium incanum 9156s.jpg
Geranium incanum 9156s.jpg
File:White pea flower.jpg
White pea flower.jpg
File:20140226Narcissus2.jpg
20140226Narcissus2.jpg
File:使君子Combretum indicum 20210523080843 01.jpg
使君子Combretum indicum 20210523080843 01.jpg
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