Lithocarpus, commonly known as the stone oaks, is a genus of approximately 340 species of evergreen trees in the beech family Fagaceae, order Fagales. The genus is concentrated in Southeast Asia, with its greatest diversity in the upland forests of Indochina, the Malayan Archipelago, and the islands as far east as Papua. Stone oaks are a dominant component of montane forests above 1,000 m (3,300 ft) elevation, filling an ecological role similar to that of Dipterocarpaceae in the lowlands.
Stone oaks are distinguished from the closely related oaks (Quercus) by several features: their flowers are insect-pollinated and borne on erect spikes, and the female flowers have notably short styles with punctate stigmas. The leaves are leathery, alternate, and almost always entire-margined. The fruit is an acorn-like nut enclosed in a basal cupule; the cupules show remarkable diversity in the arrangement of their lamellae and scales, ranging from partly enclosing to fully enclosing the nut, with a few species producing irregularly dehiscent cupules. In several sections of the genus the seed is embedded in highly lignified basal fruit material, creating an unusually hard protective structure — the origin of the genus name, from Greek λίθος (lithos, "stone") and καρπός (karpos, "seed").
The genus has a deep fossil record extending through Europe and North America from the Eocene to the Miocene, suggesting a once-cosmopolitan distribution later contracted to Asia. The North American tanoak (Notholithocarpus densiflorus) was long placed within Lithocarpus, but genetic and morphological evidence has established that its resemblance in flower and fruit structure is the result of convergent evolution; it has since been transferred to its own genus, Notholithocarpus. Lithocarpus comprises roughly 14 subgenera in Camus's treatment, with Pasania being by far the largest (about 209 species).
The seeds of some species, such as Lithocarpus edulis, have edible kernels; those of others are inedible and very bitter. Several species are cultivated as ornamental trees in parks and large gardens across warm temperate and subtropical regions.
Etymology
The genus name Lithocarpus derives from the Greek λίθος (lithos, "stone") and καρπός (karpos, "seed"), a reference to the notably hard woody shell that encases the seed in many species.
Distribution
Stone oaks range from the foothills of the Hengduan Mountains through Indochina and the Malayan Archipelago, reaching as far east as Papua across Wallace's Line. They are most abundant in upland forests above 1,000 m and are absent from the Lesser Sunda Islands, which experience seasonal droughts the genus cannot tolerate. Fossil evidence places ancestral Lithocarpus in North America and Europe from the Eocene through the Miocene.
Ecology
Lithocarpus trees are dominant components of subtropical and tropical montane forests across Southeast Asia, sharing many ecological characteristics with the Dipterocarpaceae of the lowlands. Most species are restricted to elevations above 1,000 m and are strongly intolerant of seasonal drought, which limits their distribution despite their capacity to cross significant water barriers such as Wallace's Line.
Taxonomy Notes
The North American tanoak (Notholithocarpus densiflorus) was historically included in Lithocarpus based on similarities in flower and fruit morphology, but both genetic and morphological evidence have shown these similarities are the result of convergent evolution. Tanoak now belongs to the separate genus Notholithocarpus. Within Lithocarpus, Camus recognised 14 subgenera; the largest is Pasania with approximately 209 species.
