Ecological Explainer: Head Inflorescences

Flowers come in many shapes and sizes. Sometimes a bunch of flowers grow so close together that they trick you into thinking they are one flower.
 The Birds and Bees
 So I probably don’t need to tell you that a flower is the part on the plant that holds the reproductive organs. In their simplest form you have the female organ (which includes an ovary and a landing pad for pollen) and the male organ (a little capsule that flaps around in the wind letting pollen out into the world). There are pretty petals fringing out around all this hardware. Their job is to lure the animals that are going to spread the pollen between flowers. Plant sex happens when the pollen from a male organ lands on a female landing pad, male sex cells go down into the female ovary and…BAM….fertilisation. The flower turns into a fruit and the merged sex cells turn into seeds.

 A Bouquet
 The flower I have just described is a super simplistic one. Think of a lily. But there are an infinite number of variation on this theme! We have all seen the amazing variety of colours that flowers come in. Think about the different shapes. From orchids to tulips. Some flowers are both male and female, some are either male or female. We don’t think much about it but grass has flowers. The wheat we are the fruits that develop from the very plain flowers (their pollen spreads on the wind so they don’t need to impress anyone). The flowers on a plant can be arranged in loads of different ways. When there are a bunch of flowers sitting on a stem close together it is called an inflorescence. These also come in many different forms. Today I want to talk about a type of inflorescence called a head.
 Heads Up
 For my birthday I got a microscope. One of the first things I did was pull apart a daisy ‘flower’ into its parts. So based on all the above, it may not come to you as a surprise when I tell you daisies are not a single flower, but a number of flowers arranged to look like a single larger flower. This is called a head. Each of the individual flowers is very squat and they all sit very close together. The most common group of plants with this arrangement is the daisy family (or the Asteraceae family). In this family you have 2 types of flowers that make up the head inflorescence: 1) disk flowers and 2) ray flowers. The petals we see are single petals on the ray flowers which ring around the outside of the inflorescence. Making up the middle of the head inflorescence is lots of disk flowers.


On the left a disk flower and on the right a ray flower.


And this is what it looks like when you put it all together! The curly structures sticking up out of the flowers are the female reproductive structures (called a pistil)