This is a photo I took a few evenings ago. The low sun was just peering through the hedgerow and illuminating the edges of these catkins.
I know this is a hazel tree and that these are catkins, but while I was writing this, I realised I didn't actually know much more than that... so I decided to look a few things up.
It turns out catkins are clusters of lots of small flowers, and can be male or female depending on the species of tree they come from. Hazels, however, can only have male catkins.
The female hazel flowers are hidden among the buds with only their red styles poking out to receive pollen. These flowers are wind pollinated, so they don't need features like petals to attract insects.
Despite male and female hazel flowers being found on the same tree, I've never seen the female ones before so I'm definitely going to have a closer look next time!
Technical details: Canon 7D MKII + 100mm macro lens; 1/1000 sec at f/2.8; ISO 100.