Lithocarpus

Lithocarpus Temporal range: Eocene–Recent PreꞒ Ꞓ O S D C P T J K Pg N
Lithocarpus edulis, Kantō region, Japan
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Fagales
Family:	Fagaceae
Subfamily:	Quercoideae
Genus:	Lithocarpus Blume
Species
See text
Diversity
c. 340 species
Synonyms
Pasania Oerst.

Lithocarpus is a genus in the beech family, Fagaceae. Trees in this genus are commonly known as the stone oaks and differ from Quercus primarily because they produce insect-pollinated flowers on erect spikes and the female flowers have short styles with punctate stigmas. At current, around 340 species have been described,^[1] mostly restricted to Southeast Asia. Fossils show that Lithocarpus formerly had a wider distribution, being found in North America and Europe during the Eocene to Miocene epochs.^[2] The species extend from the foothills of the Hengduan Mountains, where they form dominant stands of trees, through Indochina and the Malayan Archipelago, crossing Wallace's Line and reaching Papua. In general, these trees are most dominant in the uplands (more than 1,000 m or 3,300 ft above sea level) and have many ecological similarities to the Dipterocarpaceae, the dominant lowland tree group.^[3] These trees are intolerant of seasonal droughts, not being found on the Lesser Sunda Islands, despite their ability to cross numerous water barriers to reach Papua.^[4][5]

The North American tanoak or tanbark oak (Notholithocarpus densiflorus) was previously included in this genus but recent evidence indicates the similarities in flower and fruit morphology are due to convergent evolution. Both genetic and morphological evidence demonstrate that the tanoak is a distant relative to Asian stone oaks and, therefore tanoak has been moved into a new genus, Notholithocarpus.^[6]

Lithocarpus trees are evergreen trees with leathery, alternate leaves, the margins of which are almost always entire, rarely toothed. The seed is a nut similar to an oak acorn with a cupule enclosing the basal part of the fruit. Cupules of stone oaks demonstrate a wide variety in the type and arrangement of lamellae and scales on the outside of the cupule, with some of them completely enclosing the nut, even becoming irregularly dehiscent in a few species. The seeds are often protected by a hard woody shell (hence the genus name, from Greek λίθος, lithos, "stone" and καρπός, karpos, "seed"). In some sections of the genus, the seed is embedded in the basal material of the fruit which becomes highly lignified and hard, lending greater mechanical protection to the seed,^[7] creating a novel type of fruit.^[8] The kernel is edible in some species (e.g. Lithocarpus edulis), but inedible, and very bitter, in others.

Several of the species are very attractive ornamental trees, used in parks and large gardens in warm temperate and subtropical areas.