1. Involucre campanulate, with large, dentate, spreading lobes.
Pontica, Shrub. Leaves cordate, roundish ovate or broad-oval, doubly serrate. Involucre finely pubescent, with few glandular hairs at the base. Nut is large, broad-ovate.
Western Asia. From this species the Cob Nuts seem to have originated; also the Spanish Nuts are probably mostly cross-breeds between this species and C. Avellana or C. maxima, or between the two latter species.
2. Involucre narrowed above the nut into a beak.
maxima. (C. tubulosa). Shrub, sometimes tree, to 30 feet. Leaves cordate, roundish-ovate, slightly lobed and doubly serrate, 3-6 inches long. Involucre finely pubescent outside. Nut is oblong, large; kernel with thin red or white skin. Southern Europe. A variety is C. purpurea: leaves deep purplish red. Many varieties, with large nuts, known as Fiiberts or Lambert’s Filberts.
rostrata. Shrub, 2-6 feet. Leaves rounded or slightly cordate at the base, oval or obovate, densely serrate and sometimes slightly lobed, nearly glabrous at length, except sparingly pubescent on the veins beneath; 2.5-4 inches long. Involucre is densely beset with bristly hairs, beak long and narrow. The nut is ovoid, .5 inch long. Eastern North America; west to Minnesota and Colorado.
Californica. Allied to C rostrata. Shrub, to 20 feet. Leaves more villous beneath. Involucre with a short beak, which is
often flaring and sometimes torn.
C. heterophylla. Allied to C. Avellana. Leaves more lobed. Involucre large, spreading, longer than the fruit with large, triangular, nearly entire teeth. Northern China; Japan. (Offered by importers.)
C. Mandshurica, allied to C. rostrata. Leaves large and broad. Involucre thickly beset with strong brown bristles; tube slightly enlarged at the apex, and laciniately divided into narrow, entire segments. Japan.
C. Siéboldi, Allied to C. rostrum. Leaves narrower. Involucre densely coated with loosely appressed, less bristly hairs. Beak long and narrowed toward the end.