For a short time in the spring (late May through early June) it looks like someone has decorated the twigs of our hickory tree with green tinsel. These are the flowers on our shagbark hickory tree. For all the years I've watched our tree, I haven't paid much attention to the flowers. And yet I know they're there because every fall we've got hickory nuts. Turns out that shagbark hickories are monoecious - that means they have male flowers (the long catkins) and female flowers (tiny flowers at end of the twig). They depend on the wind for pollination.
You know what else is monoecious? Cucumbers, summer squash, melons, and pumpkin plants. If you grow any of those, take a look at their flowers this summer and see if you can tell which ones are the female flowers and which ones are the male flowers.