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Trees in the genus Carya (from Ancient Greek kary “nut”) are commonly known as Hickory. The genus includes 17-19 species of deciduous trees with pinnately compound leaves and large nuts. A dozen or so species are native to North America (11–12 in the United States, 1 in Mexico), and 5–6 species from China and Indochina.
Another Asian species, Beaked Hickory, previously listed as Carya sinensis, is now treated in a separate genus Annamocarya, as Annamocarya sinensis.
Hickory flowers are small yellow-green catkins produced in spring. They are anemophilous 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, thin in a few, notably C. illinoinensis; it is divided into two halves which split apart when the seed germinates.
In the APG system, genus Carya (and the whole Juglandaceae family) has been recently moved to the Fagales order.
Hickory is used as a food plant by the larvae of some Lepidoptera species. These include:
Another insect that uses the hickory tree as a food source is the hickory leaf stem gall phylloxera (Phylloxera caryaecaulis). Phylloxeridae are related to aphids and have a similarly complex life cycle. Eggs hatch in early spring and the galls quickly form around the developing insects. Phylloxera galls may damage weakened or stressed hickories, but are generally harmless. Deformed leaves and twigs can rain down from the tree in the spring as squirrels break off infected tissue and eat the galls, possibly for the protein content of the phylloxera, or possibly because the galls are fleshy and tasty to the squirrels.