Walnut trees are any species of tree in the plant genus Juglans, the type genus of the family Juglandaceae, the seeds of which are referred to as walnuts. All species are deciduous trees, 10–40 metres (33–131 ft) tall, with pinnate leaves 200–900 millimetres (7.9–35.4 in), with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts (Pterocarya), but not the hickories (Carya) in the same family.
Juglans regia, the Persian walnut, English walnut, Carpathian walnut, Madeira walnut, or especially in Great Britain, common walnut, is an Old World walnut tree species native to the region stretching from the Balkans eastward to the Himalayas and southwest China. The largest forests are in Kyrgyzstan, where trees occur in extensive, nearly pure, walnut forests at 1,000–2,000 m (3000 to 7000 ft) altitude —notably at Arslanbob in Jalal-Abad Province. It is widely cultivated across Europe.
Juglans major (literally, the larger walnut), also known as Arizona walnut, is a walnut tree which grows to 50 ft tall (15 m) with a DBH of up to 0.61 metres (2 ft) at elevations of 300–2,130 m (1,000–7,000 ft) in Texas, Oklahoma, New Mexico, Arizona, and Utah. It also occurs in Mexico as far south as Guerrero. Common names include Arizona black walnut (as it belongs to the "black walnuts" section Juglans sect. Rhysocaryon), and the Spanish name nogal cimarrón (cimarron walnut).
Juglans ailantifolia (synonyms J. cordiformis and J. sieboldiana and J. mandshurica var. sachalinensis), the Japanese walnut (Japanese: 鬼胡桃 oni-gurumi), is a species of walnut native to Japan and Sakhalin. It is a deciduous tree growing to 20 m (66 ft) tall, rarely 30 m (98 ft), and 40–80 cm stem diameter, with light grey bark. The leaves are pinnate, 50–90 cm long, with 11-17 leaflets, each leaflet 7–16 cm long and 3–5 cm broad. The whole leaf is downy-pubescent, and a somewhat brighter, yellower green than many other tree leaves. The male flowers are inconspicuous yellow-green catkins produced in spring at the same time as the new leaves appear. The female flowers have pink/ red pistils. The fruit is a nut, produced in bunches of 4-10 together; the nut is spherical, 3–5 cm long and broad, surrounded by a green husk before maturity in mid autumn.
Juglans boliviana, the Bolivian walnut, is a tree in the family Juglandaceae and the walnut genus (Juglans ). According to Manning's 1960 revision, it occurs in the Andes of northern Bolivia and central and southern Peru. Manning included the species Juglans peruviana, described by Dode in 1909 from nuts collected at an unknown locality in Peru, because the nuts closely match those of J. boliviana and apparently came from Metraro, where only J. boliviana is known.
Juglans hindsii, commonly called the Northern California walnut and Hinds' black walnut, is a species of walnut tree endemic to Northern California. It is commonly called claro walnut by the lumber industry and woodworkers, and is the subject of some confusion over its being the root stock for English walnut orchard stock.
Juglans microcarpa, known also as the little walnut, Texas walnut, Texas black walnut or little black walnut (as it belongs to the "black walnuts" section Juglans sect. Rhysocaryon), is a large shrub or small tree (10–30 ft tall) which grows wild along streams and ravines in Texas, New Mexico, Oklahoma, and Kansas. It produces nuts with a width of 1/2—3/4 in. The pinnately compound leaves bear 7—25 untoothed to finely-toothed leaflets, each 1/4—1/2 in wide. It is found at elevations ranging from 700 ft to 6700 ft.
Juglans mandshurica, the Manchurian walnut, is a deciduous tree of the genus Juglans (section Cardiocaryon), native to the Eastern Asiatic Region (China, Russian Far East, North Korea and South Korea ). It grows to about 25 m.
Juglans neotropica is a species of plant in the Juglandaceae family. It is found in Colombia, Ecuador, and Peru. It is threatened by habitat loss. Common names include Colombian walnut, Ecuadorian walnut, Andean walnut, nogal, cedro negro, cedro nogal, and nogal Bogotano.