Hickory (empty nut husks)

Hickory flowers are small, yellow-green catkins produced in spring. They are wind-pollinated and self-incompatible. The fruit is a globose or oval nut, 2–5 cm long and 1.5–3 cm diameter, enclosed in a four-valved husk, which splits open at maturity. The nut shell is thick and bony in most species, and thin in a few, notably C. illinoinensis; it is divided into two halves, which split apart when the seed germinates.