Hickory nuts grew thicker shells as defence against rodents
Fossil hickory nuts have thinner, simpler shells than living species, pecans excepted. The likeliest explanation is an evolutionary arms race: over millions of years, trees whose seeds resisted gnawing rodents left more descendants. Today most hickories wrap their nuts in thick, bony shells inside a four-part husk.
Carya, the hickories, is a genus of 19 species in the walnut family. Twelve are native to North America and seven to China, Indochina and Assam in northeastern India. The English name was clipped from an Algonquian word, perhaps Powhatan, something like pocohicora, possibly naming the nut or a milky drink made from it. Carya itself is the Greek for nut. Most species drop their leaves, but one in southeast Asia, C. sinensis, is evergreen.
The genus has a long, shrinking history. The oldest attributed fossils are Cretaceous pollen grains from Mexico and New Mexico, and modern Carya appears in rocks 34 million years old. Hickories once ranged across the Northern Hemisphere, but the Pleistocene ice ages wiped them from Europe, and in Anatolia they lingered until the early Holocene, probably ending through human disturbance. North American hickories vanished entirely west of the Rocky Mountains, where a Miocene species from Washington State survives only as fossils.
Botanists argue over what the fruit is. Because hickory and walnut nuts grow inside a husk, some call them drupe-like trymas rather than true nuts, although the Angiosperm Phylogeny Group treats them as nuts. The flowers are wind-pollinated catkins and cannot fertilise themselves, so growers must plant at least two cultivars, since grafted clones of one variety cannot pollinate each other.
Hickory fed people long before orchards. Indigenous peoples of the Eastern Woodlands relied on the nuts from the middle Archaic period, and the Cherokee used them in Kanuchi soup, pressed them for oil and made green dye from the bark. Dried nuts are about 64 percent fat. Shagbark bark yields a smoky syrup like maple syrup, and ash from burnt hickory wood once made strong lye for soap. The caterpillar of the regal moth, nicknamed the hickory horn-devil, feeds on its leaves.
Source: Hickory
