The evolution of flowers: a floral adventure for curious kids

Pollination in flowers

When pollen lands on the stigma (the tip of a female pistil) it creates a tube into the style that leads to the ovary and allows the male cells inside the pollen to travel to the female ovules. This is called pollination and is very important for most flowering plants. It leads to fertilisation (where the male and female cells fuse) and the formation of seeds containing plant embryos.

So, flowers hold essential reproductive organs. This is very important to the flower. But what do you notice first when you look at a flower?

Pretty petals

With most flowers, it’s the petals that grab your attention. Petals have an amazing array of shapes, colours, patterns, scents, and even surface textures. 

Why do flowers go to such trouble?

The job of petals is to attract animals that can carry the flower’s pollen from its anthers to the stigma of another of its flowers, which allows pollination to happen.

That’s not to say all flowers are so showy. The plants with the least showy flowers (like grasses) usually rely on the wind for pollination and so don’t need to go out of their way to make fancy petals that attract animals.

Those that rely on animals, though, have to keep up appearances.

A bee covered in pollen. Image credit: Myriam Zilles.

What’s in it for the pollinators?

Pollinators don’t usually visit flowers just because they look nice.

Some, like the bumblebee, are there to eat pollen. It’s a rich source of protein. But flowers have evolved another trick to ensure a steady stream of animals that will carry their pollen far and wide.

Flowers make a sugary liquid, called nectar, that pollinators love to feed on.

Watch the hummingbird feed on nectar in this clip from BBC Earth: 

So what does this nectar have to do with what the flowers look like?

The tricks and treats of flowers

Pollinators learn where they can get nectar by recognising the flowers – by colour, shape, pattern and smell. They find the ones they like best and remember what they look and smell like. Some petals also have cells on the surface shaped like cones that make it easier for bees to maintain their grip and stay on the flower.

As fancy as they look to us, flowers have evolved even more signals to pollinators than we can see. Some of the patterns on petals are only visible in ultraviolet, which bees can see but we can’t.

The patterns, colours and textures on the petals also act like signposts to guide pollinators to the centre of the flower. The centre is where all the important work happens: it’s where the nectar is kept, where the pollen is waiting and where pollination happens. Bees can even feel changes in the shape of the cells on the petal’s surface as they get closer to the centre of the flower.

Sunflowers are famous for tracking the sun during the day. One of the benefits they get from this is that the extra warmth helps them to attract bees. The evolution of flowers is full of surprises.

This short video gives a nice summary of how this works:

Sneaky flowers

Some flowering plants have evolved very sneaky ways to entice pollinators.

Flowers have evolved mimicry

There are flowers that look like insects and some, in an astounding feat of evolution, even imitate rotting meat!

Mimicry in flowers. The carrion flower in the genus Rafflesia (left) looks and smells like rotting meat. The fly orchid (top right) and bee orchid (bottom right) look like insects.

That’s right. Carrion flowers look and smell like rotting meat, they even generate heat that mimics the heat of decay. This attracts insects that are looking for a good place to lay their eggs, and while they do this they also pollinate the flowers.

Some of these flowers also have traps for the insects that load them with pollen before releasing them. These are not the kind of flowers you want to keep in your home!

Flowers have evolved hearing

Flowers can also hear their pollinators. 

Evening primroses

Yep. Plants actually do have “ears”. 

Evening primroses can sense the buzzing of bees nearby. What do they do with this information? They make their nectar sweeter for the bees. Kind of them. And sneaky.

Flowers have evolved to masquerade as one

In another remarkable feat of sneakiness, and more recent evolution of floral complexity, many of the beautiful blooms we enjoy are not actually single flowers at all. They are composite flowers.

Composite flowers are clusters of flowers that work together to look like one large flower, making them more enticing to pollinators. If you haven’t noticed this before (I hadn’t) then prepare to be amazed. My daughter showed a large degree of skepticism towards the idea so here are a few photos of composite flowers as evidence to show your child:

Examples of composite flowers including members of the daisy family and dandelions.

Composite flowers include all the lovely daisy flowers and sunflowers. That central disc in a daisy or sunflower? It’s actually a huge cluster of teeny tiny flowers, each with an ovary that produces a seed, surrounded by more showy flowers with larger petals around the outside to draw the insects.

Dandelions are another example of these composite flowers. Each of the tiny flowers in the centre produces one of the dandelion’s characteristic parachute seeds in the dandelion clocks that are so fantastic at attracting children (who happily help to disperse them).

Flowers are mathematical wonders

If you look closely at the head of a sunflower you’ll notice the amazing order to the tiny flowers, and the seeds they produce after pollination, in the central disk. The seeds are arranged into two sets of spiral arms winding in opposite directions from the centre out.

This arrangement is a well-known mathematical wonder of nature that has been used in many places in the evolution of flowers, and other life on Earth. It’s a fantastic topic to explore with curious kids, especially those that enjoy maths, sorting and ordering. Stay tuned for a separate post on the Fibonacci sequence in nature.