Key to Genera and Species — Part 1

A. Pith of twigs chambered; husk not opening at maturity; nuts not smooth.

I. Genus JUGLANS, Linn.

B. Fruit elongated, clammy, in racemes; heart wood light brown. (J. cinerea) BUTTERNUT

BB. Fruit globular, not clammy; solitary or paired; heart wood dark brown.

C. Nuts deeply and irregularly ridged, large. (J. nigra) BLACK WALNUT

CC. Nuts deeply furrowed, small, thick shelled. (J. rupestris) MEXICAN WALNUT

CCC. Nuts faintly furrowed, small, thin shelled. (J. Californica) CALIFORNIA WALNUT

AA. Pith of twigs solid; husk opening by 4 valves; nuts smooth.