Last month I discovered that some friends had a number of hazelnut shrubs (Corylus sp., Betulaceae) growing on their property. While I’ve never been crazy about hazelnuts or hazelnut confections, I found the plants themselves to be interesting.
Hazels are monoecious, meaning that each plant produces both male and female reproductive organs. The male structures are catkins that grow in the fall, persist through the winter, and then flower the following spring. The male flowers pollinate the female flowers, which upon fertilization develop over the summer into the familiar nuts.
Each developing nut is protected by a leafy husk called an involucre. The size, shape, and arrangement of the involucres can be used to help distinguish the various species. Regardless of the species all hazelnuts are edible. Commercially the common hazel (Corylus avellana) is preferred, probably due to nut size, yield, ease of cultivation, and flavor.