Castanopsis (chinquapin or chinkapin) is a genus of evergreen trees belonging to the beech family, Fagaceae. The genus contains about 120 species, which are today restricted to tropical and subtropical eastern Asia. A total of 58 species are native to China, with 30 endemic; the other species occur further south, through Indochina to Indonesia, and also in Japan. The English name chinkapin is shared with other related plants, including the golden chinkapins of the Pacific United States, which are sometimes included within Castanopsis but are more often considered a separate but very closely related genus, Chrysolepis.
They show many characters typical of Fagaceae. They are at least large shrubs but some species grow into sizeable trees. Their leaves are usually tough and much sclerotized and have a well-developed cuticula. Their flowers are unisexual, and the male ones are borne in erect catkins. The epigynous female flowers produce a single seed each but are congregated in small clusters. The fruit is a calybium, the kind of encased nut typical of Fabaceae. The calybium (nut) resembles a pointed acorn; the cupule (casing) is hard like that of beechnuts and spiny like that of chestnuts. Three thickened ridges run the length of the calybium's shell.
Plants of this genus grow on many soil types, as long as they are not calcareous. Several species have adapted to podsolic, peat bog, swamp and other acidic and/or wet soils, or to the poor dry soils common in arid habitat. Around the Oligo-Miocene boundary, Castanopsis grew abundantly along rivers and in bogs and swamps of then-subtropical Europe. The prehistoric plant community Castanopsietum oligo-miocenicum is the source of much of the lignite ("brown coal") deposits in Western and Central Europe.
Most species yield valuable timber but some have become rare due to unsustainable logging, C. catappaefolia is even in danger of extinction. As noted above, however, perhaps the most important use for Castanopsis wood is in its fossil form. 175,400 metric tons of lignite - much of which which was former chinkapin trees - were mined in Germany in 2001.
As with many Fagaceae, the nuts of many Castanopsis species are edible. The trees may be grown for their nuts, but more often they are used as forestry or ornamental trees and the nuts are collected opportunistically. Among many animals, such as tits, corvids, rodents, deer and pigs, the nuts are popular as food too.
Meguro, Tokyo and Matsudo, Chiba in Japan use shii (椎; Castanopsis cuspidata) as one of their municipal symbols. The well-known and commercially important shiitake mushroom likes to grow on the logs of C. cuspidata and derives its common name from this: shii-take simply means "Castanopsis cuspidata mushroom".
These are known and identifiable from their fruit. It is not entirely clear if they belong here or into Chrysolepis, but the pattern of biogeography - with the two genera being most diverse around the Pacific but absent from North America east of the Rocky Mountains suggests that they are indeed correctly assigned to Castanopsis. In addition, two form taxa refer to the remains of these trees, at least in part: the fossil wood Castanoxylon eschweilerense and the fossil pollen Tricolporopollenites cingulum ssp. pusillus.