Walnut Classification and Species

Species and classification

• Sect. Juglans. Leaves large (20-45 cm) with 5-9 broad leaflets, hairless, margins entire. Wood hard. Southeast Europe to central Asia.
  • Juglans regia L. (J. duclouxiana Dode, J. fallax Dode, J. orientis Dode) - Persian Walnut, Carpathian, or Common Walnut
  • Juglans sigillata Dode - Iron Walnut (doubtfully distinct from J. regia)
• Sect. Rhysocaryon. Leaves large (20-50 cm) with 11-23 slender leaflets, finely pubescent, margins serrated. Wood hard. North America, South America.
  • Juglans australis Griseb. (J. boliviana Dode) - Argentine Walnut
  • Juglans brasiliensis Dode - Brazilian Walnut
  • Juglans californica S.Wats. - California Walnut
  • Juglans hindsii (Jepson) R.E.Smith - Hinds' Walnut
  • Juglans hirsuta Manning - Nuevo Leon Walnut
  • Juglans jamaicensis C.DC. (J. insularis Griseb.) - West Indies Walnut
  • Juglans major (Torrey) Heller (J. arizonica Dode, J. elaeopyron Dode, J. torreyi Dode) - Arizona Walnut
    • Juglans major var. glabrata Manning
  • Juglans microcarpa Berlandier (J. rupestris Engelm.) - Texas Walnut or Little Walnut
    • Juglans microcarpa var. stewartii (Johnston) Manning
  • Juglans mollis Engelm. - Mexican Walnut
  • Juglans neotropica Diels (J. honorei Dode) - Andean Walnut
  • Juglans nigra L. - Black Walnut
  • Juglans olanchana Standl. & L.O.Williams -
  • Juglans peruviana Dode - Peruvian Walnut
  • Juglans soratensis Manning -
  • Juglans steyermarkii Manning - Guatemalan Walnut
  • Juglans venezuelensis Manning - Venezuela Walnut
• Sect. Cardiocaryon. Leaves very large (40-90 cm) with 11-19 broad leaflets, softly downy, margins serrated. Wood soft. Northeast Asia, eastern North America.
  • Juglans ailantifolia Carr. (J. cordiformis Maxim., J. sieboldiana Maxim.) - Japanese Walnut
  • Juglans cinerea L. - Butternut
  • Juglans mandschurica Maxim. (J. cathayensis Dode, J. formosana Hayata, J. hopeiensis Dode, J. stenocarpa Maxim.) - Chinese Walnut or Manchurian Walnut

The best-known member of the genus is the Persian Walnut (Juglans regia), native from the Balkans in southeast Europe, southwest & central Asia to the Himalaya and southwest China.

The scientific name Juglans is from the Latin jovis glans, "Jupiter's nut", and regia, "royal". Its common name, Persian walnut, indicates its origins in Persia (Iran) in southwest Asia; 'walnut' derives from the Germanic wal- for "foreign", recognising that it is not a nut native to northern Europe. In Kyrgyzstan alone there are 230,700 ha of walnut-fruit forest, where J. regia is the dominant overstorey (Hemery and Popov 1998). This is the species which is widely cultivated for its delicious nuts. J. regia is also called English walnut because English merchant marines once controlled its world commerce.

The Black Walnut (Juglans nigra) is a common species in its native eastern North America, and is also widely cultivated elsewhere. The nuts are edible, but have a smaller kernel and an extremely tough shell, and they are not widely grown for nut production.

The Butternut (Juglans cinerea) is also native to eastern North America, where it is currently endangered by an introduced disease, butternut canker, caused by the fungus Sirococcus clavigignenti. Its leaves are 40-60 cm long, and the nuts oval.

The Japanese Walnut (Juglans ailantifolia) is similar to Butternut, distinguished by the larger leaves up to 90 cm long, and round (not oval) nuts.

Walnut Hybrids

• Juglans x bixbyi Rehd. - J. ailantifolia x J. cinerea
• Juglans x intermedia Carr. - J. nigra x J. regia
• Juglans x notha Rehd. - J. ailantifolia x J. regia
• Juglans x quadrangulata (Carr.) Rehd. - J. cinerea x J. regia
• Juglans x sinensis (D. C.) Rehd. - J. mandschurica x J. regia
• Juglans x paradox Burbank - J. hindsii x J. regia
• Juglans x royal Burbank - J. hindsii x J. nigra