A Key to Some Seedlings of Walnuts

W. C. Muenscher and Babette I. Brown

Cornell University, Ithaca, N. Y.

While working with the seedlings of several species of walnuts certain diagnostic characters, by which the common species can be separated, became evident. These characters have been used to make a key to seedlings from one to three months of age. This key has been found helpful to us and it is here presented in the hope that it may prove useful to others who need to handle and determine walnuts in the seedling stage.

The key has two main divisions based upon the types of leaves on the main axis. The first division includes three species, Juglans sieboldiana, Japanese butternut, J. cinerea, American butternut, and J. regia, Persian or English walnut, all of which have only compound green leaves. In addition, one or more pairs of minute simple scales or buds occur on the lower part of the stem but above the cotyledons. The second main division includes species in which the seedlings have several simple, alternate, scale-like leaves followed successively by serrate, lobed and finally compound leaves forming a gradual series. This group includes Juglans rupestris, Texas black walnut, J. nigra, eastern black walnut, J. honorei, Ecuador walnut, J. pyriformis, Mexican walnut, J. major, Arizona black walnut, J. californica, California black walnut, and J. hindsii, Hind's black walnut.

It is important that the leaves on the primary axis arising from the plumule are examined. If the primary axis is injured secondary shoots may arise from the axils of the cotyledons. These may develop various types of leaves not necessarily like those of the primary axis. The key is based upon seedlings grown in the field and in the greenhouse at Ithaca, New York.

A Key to seedlings of some species of Juglans 1. Leaves on the primary axis all compound; 1 to 4 pairs of opposite or subopposite reduced scales or buds sometimes present on the lower axis but above the cotyledons. 2. Scales or buds wanting between the lowest compound leaves and the leaves and the cotyledons J. sieboldiana 2. Scales or buds in pairs on 1 to 4 nodes below the compound leaves. 3. Stem with 1 pair of opposite scales or buds near the base; leaflets hairy, serrate J. cinerea 3. Stem with 2 to 4 pairs of opposite scales or buds below the compound leaves; leaflets glabrous, entire or denticulate J. regia 1. Leaves on the primary axis alternate, forming a gradual series from simple, entire scales to compound leaves; the lower 3 to 8 leaves simple. 4. Lateral veins of leaflets all or mostly all terminating in the notches between marginal teeth J. rupestris 4. Lateral veins of leaflets or their main branches all or mostly all terminating in the apex of marginal teeth. 5. Midrib of leaflets glandular hairy. 6. Glandular hairs on midrib of young leaflets interspersed with stellate clusters of gray glandless hairs; lateral leaflets ovate to broadly lanceolate, rugose J. nigra 6. Glandular hairs on midrib of young leaflets interspersed with sessile, usually yellow glands; lateral leaflets lanceolate, not rugose J. honorei 5. Midrib of leaflets glabrous or nearly so, sometimes with scattered, sessile glands. 7. Leaflets lanceolate, with acuminate apex; rhachis glabrous. 8. Leaflets widest near middle; vein-islets prominently raised; free ends of veins wanting or if present distinct to the apex and mostly unbranched J. pyriformis 8. Leaflets mostly widest below the middle; vein-islets not prominently raised; free ends of veins slender, terminating in indistinct branches J. major 7. Leaflets ovate or nearly so, with obtuse or acute apex; rhachis somewhat pubescent. 9. Petioles of the 3 lower compound leaves less than 1 cm. long; leaves crowded on a short axis J. californica 9. Petioles of the lower compound leaves from 1+ to 3 cm. long; leaves more distant on an elongated axis J. hindsii