This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Male flowers in simple catkins, having a calyx of 3 to 6 irregular lobes, and usually numerous (more than 8) stamens. The fleshy fibrous epicarp of the fruit bursting irregularly, endo-carp or shell 2-valved, usually with deep furrows. The species are from North America and the mountains of Asia. The name is a corruption of Jovis glans, literally Jupiter's Nut.
1. J. regia. Common Walnut. - This handsome and useful tree needs no description; but we may call attention to some of the better varieties. Those most valued for their nuts are the Highflyer, Titmouse, or tenera (thin-shelled), and serotina, the latter being valuable on account of its flowering season being a month later than the ordinary form, and thus escaping the Spring frosts. There is also a very large-fruited variety called the Double Walnut, whose shells are often polished and hinged, and rilled with trinkets. The varieties most esteemed for their foliage besides the ordinary one are laciniata, hetero-phjjlla, variegata, monophylla, and aspleniifdlia. The names are sufficiently descriptive of the peculiarities of the several varieties. Native of Asia, from the Caucasus to China.
J. nigra, Black Walnut, is an erect tall-growing tree, with more numerous toothed leaflets hairy beneath, and a more persistent husk. Nut spherical, corrugated, edible, but not equal to the common Walnut. It is a native of the Western States of North America. There are some varieties of this, and one called intermedia, supposed to be a hybrid between this and the foregoing. J. cinerea, Butternut, is also a North American species. It has greyish bark, glutinous branches, and. oblong fruits with only one partition at the base.