Carpinus and Ostrya are very similar in foliage ; and the following key, based upon the characters of the leaves and branches (Plate 201), distinguishes all the species of both genera which are in cultivation in England. Carpinus laxiflora, though not yet introduced, has been included, as it has been much confused with the other Japanese hornbeams.
Key to Carpinus and Ostrya
I. Leaves not exceeding 2 inches in length.
- 1. Carpinus orientals, Miller. South-eastern Europe, western Asia.
- Leaves 1½ inch long, acute, deeply plicate.
- 2. Carpinus polyneura, Franchet. Central China.
- Leaves 2 inches long, acute, smooth and only slightly plicate.
II. Leaves exceeding 2 inches in length.
A. Leaves lanceolate.
- 3. Carpinus japonica, Blume. Japan.
- Leaves about 4 inches long, much longer in proportion to their width than in the other species, with numerous (eighteen to twenty-four pairs) nerves.
B. Leaves ovate, acute at the apex.
- 4. Carpinus yedoensis, Maximowicz. Central China. Cultivated in Japan.
- Leaves 2½ inches long, rounded at the base, with conspicuous bands of appressed pubescence on the upper surface. Branchlets pilose.
C. Leaves ovate, acuminate at the apex.
* Leaves deeply cordate at the base.
- 5. Carpinus cordata, Blume. China, Korea, Manchuria, and Japan.
- Leaves 4 to 5 inches long, broad in proportion to their length, with fifteen to twenty pairs of nerves.
** Leaves rounded or only slightly cordate at the base.
† Under surface glabrous between the nerves.
- 6. Carpinus laxiflora, Blume. China, Japan.
- Leaves 2½ inches long, rounded at the base, abruptly contracted into a very long acuminate apex. Branchlets with scattered long hairs. Buds minute, 1⁄16 inch long.
- 7. Carpinus Betulus, Linneus. Europe, western Asia.
- Leaves 3 inches long, slightly cordate at the base, turning yellow in autumn. Branchlets with scattered long hairs. Buds fusiform, ¼ to ⅓ inch long.
- 8. Carpinus caroliniana, Walter. North America.
- Leaves as in C. Betudus, but turning red in autumn. Branchlets with scattered long hairs. Buds ovoid, ⅛ inch long.
†† Under surface pubescent between the nerves.
- 9. Ostrya carpinifolia, Scopoli. Southern Europe, Asia Minor, Syria.
- Leaves 3 inches long, not velvety to the touch above, rounded at the base. Branchlets with dense appressed pubescence.
