It’s easy to see why the Costaceae wound up classified as they did. Take a look at the flowers below, which all belong to different species of Costaceae. If you had to sort them into three different groups, how would you do it?
![Top, left to right: Cheilocostus speciosus, Tapeinochilos ananasse, Costus guaniensis. Bottom, left to right: Costus afer, Costus letestui, Costus erythrocoryne.](https://evolution.berkeley.edu/wp-content/uploads/2021/06/Costaceae.jpg)
Most people would probably put the two white-flowered species together, the two spiky, red-flowered species together, and the two pink-flowered species together. However, a quick glance at the positions of these species on the phylogeny below reveals that flower form is not a very good indicator of evolutionary history — some species with similar flowers are not very closely related at all. To understand why this is the case, you need to know a little bit about the function of flowers, as well as the birds and the bees.
Dig deeper: find out what makes a petal a petal.
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