Skip to main content
ARS Home » Pacific West Area » Davis, California » Nat'l Clonal Germplasm Rep - Tree Fruit & Nut Crops & Grapes » Docs » Juglan Page » Main

headline bar



The walnut




To view the attached article, you will need Adobe Acrobat.  Click on the link below to download a free copy (non-federal site.)



Molecular phylogeny of Juglans (Juglandaceae): a Biogeographic Perspective


Juglans L. is principally a New World genus in the family Juglandaceae comprising about 21 extant deciduous tree species occurring over North and South America, the West Indies, and southeastern Europe to eastern Asia and Japan (Manning, 1978), and exhibits disjunct distributional patterns between eastern Asia and eastern North America (Manchester, 1987; Fig. 1).  The genus is divided into four sections, based mainly on the morphology (Dode, 1909ab; Manning, 1978).  Section Rhysocaryon (black walnuts), which is endemic to the New World, comprises five North American temperate taxa: J. californica S. Wats., J. hindsii (Jeps.) Rehder, J. nigra L., J. major (Torr. ex Sitgr.) Heller, and J. microcarpa Berl.; three Central American subtropical taxa: J. mollis Engelm., J. olanchana Stadl. & I. O. Williams, J. guatemalensis Mann.; and two South American tropical taxa, J. neotropica Diels, and J. australis Griesb, mainly occurring in the highlands.  They typically bear four-chambered nuts with thick nutshells and septa. Section Cardiocaryon (Asian butternuts) contains four taxa: J. hopeiensis Hu, J. ailantifolia Carr., J. mandshurica Maxim., and J. cathayensis Dode,all native to East Asia, while section Trachycaryon consists of the only North American butternut taxon, J. cinerea L.  Butternuts possess two-chambered nuts with thick nutshells and septa.  Section Juglans includes two taxa: the cultivated Persian or English walnut, J. regia L., occurring naturally in the Balkan, north Iran, Turkey, the south Caspian region, central Asia, the Himalayas, and China, and bears four-chambered nuts with thin nutshells and papery septa, and cultivated throughout the subtropical regions of the World.  The second one is called iron walnut, J. sigillata Dode, which is restricted to southern China and Tibetan regions bears thick rough-shelled nuts and the characteristic dark-colored kernels (Dode, 1909a), and often considered as an ecotype of J. regia, but some botanists have treated it as a separate species.  Complete descriptions of the morphological variation, ecological distribution, and taxonomic treatment of the genus Juglans are found in Manning (1957, 1960, 1978). 


Use GRIN Global to search for more information on Juglans and the accessions in the National Plant Germplasm System (NPGS).


Questions about our walnut collection can be directed to John Preece


Links to non-federal walnut related sites:


California Walnuts

University of Georgia

Texas Walnuts

Northern Nut Growers


Some information for this page was obtained from:


Dode, L. A. 1909a. Contribution to the study of the genus Juglans (English translation by R.E. Cuendett). Bulletin of the Society of Dendrology, France 11: 22-90.

Dode, L. A. 1909b. Contribution to the study of the genus Juglans (English translation by R.E. Cuendett). Bulletin of the Society of Dendrology, France 12: 165-215.

Manchester, S. R. 1987. The fossil history of Juglandaceae. MissouriBotanical Garden Monograph 21: 1-137.

Manning, W. E. 1957. The genus Juglans in Mexico and Central America. Journal of Arnold Arboretum 38: 121-150.

Manning, W. E. 1960. The genus Juglans in South America and West Indies. Brittonia 12: 1-26.

Manning, W. E. 1978. The classification within the Juglandaceae. Annals of MissouriBotanical Garden 65: 1058-1087.


Crop Pages

Actinidia(kiwifruit)   Diospyros(persimmon)   Ficus(fig)    Juglans (walnut)   Olea(olives)   Morus (mulberry)   Pistacia(pistachio)   Prunus (peach, plum, apricot, cherry, almond, and related species)   Punica (pomegranate)   Vitis (grape) 


GRIN Accession Query