The calybium (nut) resembles a pointed acorn; the cupule (casing) is hard like that of beechnuts and spiny like that of chestnuts.

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[verification needed] suggests that they are indeed correctly assigned to Castanopsis.

The fossil cupule (upper part of the acorn) is globose with branched spines, and a broadly ovate nut scar.

Castanopsis praefissa shows the closest affinity to C. fissa, and C. praeouonbiensis closely resembles C. ouonbiensis.

Castanopsis praeouonbiensis and C. praefissa became extinct in this area because of the cooling climate from the late Miocene to the present day in Zhejiang Province.

In their rather circumscribed area of occurrence, Castanopsis are able to inhabit a wide range of temperate to tropical habitat and are often keystone species in their ecosystems.

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.