Zelkova serrata

Zelkova serrata (Japanese zelkova, Japanese elm or keyaki; Japanese: Ju (keyaki) keyaki /Gui (tsuki) tsuki; Chinese: Ju Shu /Ju Shu jushu; Korean: neutinamu neutinamu) is a species of the genus Zelkova native to Japan, Korea, eastern China and Taiwan. It is often grown as an ornamental tree, and used in bonsai. There are two types: Zelkova Serrata var. serrata is found in Japan and the mainland of eastern Asia. Zelkova Serrata is found elsewhere. tarokoensis (Hayata) Li on Taiwan which differs from the type in its smaller leaves with less deeply cut serration on the margins.

Description

Zelkova serrata is a medium-sized deciduous tree usually growing to 30 m (98 ft) tall. It is characterized by a short trunk dividing into many upright and erect spreading stems forming a broad, round-topped head. The tree grows rapidly when young though the growth rate slows to medium upon middle age and maturity.

It has alternately arranged leaves growing to 5 cm long and broad. The leaves themselves are simple and ovate to oblong-ovate with serrated or crenate margins, to which the tree owes its specific epithet serrata. The leaves are acuminate or apiculate, rounded or subcordate at the base, and contain 8-14 pairs of veins. The leaves are rough on the top, and glabrous (or nearly glabrous) on their undersides. The leaves are usually green or dark green on the top and glabrous, or nearly glabrous, on their undersides. In autumn, they turn to yellows, oranges, and reds. The petioles are

2-5 mm (1/16–3/16 in) long.

Zelkova serrata is monoecious. It develops flowers in spring with the leaves. Buds are ovoid, acutish, with many imbricate, dark brown scales. They split at a 45-degree angle from the stem. Stamina flowers are short pedicellate, approximately 3mm in size and clustered in axils between the lower leaves. Pistillate flowers appear in the axils or few of the upper leaves. They are usually approximately 1.5 mm in size and solitary. They are not showy and appear in tight groups along new stems. The drupes are small, ovate and wingless, and ripen from late summer through autumn. The drupe is green maturing to brown, subsessile and 2.5 to 3.5 mm (3/32 to 1/8 in) in diameter.

To identify Zelkova serrata, one would look for a short main trunk, low branching and a vase-shaped habit. The twigs have small, conical, dark brown buds that are in a zigzag shape. The branches are often glabrous. The bark can be grayish-brown to grayish brown. It can be smoothened with lenticels, or it can be exfoliated in patches to expose the orange inner bark. Branchlets range in color from brownish-purple brown.

Cultivation

This tree requires full to partial sun and prefers moist, well-drained soils. A fertilizer rich in potassium and nitrogen encourages new vegetation and floral buds. It can withstand heat, low water, nutrient-poor soils, and different pH levels. To allow sunlight into the inner canopy, it should be thinned periodically. Zelkova Serrata is propagated by seeds, rooted stem cuttings and grafting. Although seeds germinate easily without any pretreatment, the percentage of those who germinate is higher if stratified at 5 degrees Celsius (41 degrees F) for 60 days. Because germination requires stratification, the seed is best sown early in the year. It may be necessary for the tree to be potted and grown in a greenhouse during its first winter. It may be reintroduced into its permanent habitat after the final frost.