December 9
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Plant Genus of the family Ulmaceae

Genus Description Cultivation
Celtis Gardeners and naturalists familiar with the deciduous nettle-trees of Europe and temperate Asia, or with the hackberries of North America, often do not realize that these are outlying members of the large, mainly tropical and mainly evergreen genus Celtis, consisting of over 100 species occurring in all continents and many larger islands. Belonging to the elm family, the genus shares with Ulmus the characteristic leaf shape with usually toothed margins and asymmetric base. Each leaf has 2 stipules attached where it joins the twig and in some of the evergreen species these are modified into spines. Flowers are greenish and inconspicuous with male and female separate but on the one tree, and are followed by small berry-like fruit with thin but sugary flesh concealing a hard stone; in most species they ripen to black or dark brown. The fruits are greedily eaten by birds such as pigeons, which effectively disperse the seeds through their droppings. Some species have become troublesome weed trees when cultivated outside their native lands. CULTIVATION: They are mostly vigorous growers that adapt well to tough environments such as urban streets and parks, tolerating a wide range of soil conditions. The deciduous species make fine shade trees, needing little or no shaping and maintenance. Propagate from seed, which in the case of temperate species should be cold-stratified for 2 to 3 months before sowing in spring; germination is often erratic.
Planera Native to southeastern USA, this single-species genus contains a deciduous elm-like tree with ovate serrated leaves. The insignificant petal-less flowers of different sexes appear with new leaves and are followed by a single nut-like drupe with a hard or crusty shell. It is planted mainly as a shade tree in areas with hot summers. CULTIVATION: Frost tender, it requires a warm, humid climate and does best in a protected position in moist, well-drained soil in full sun or partial shade. It will tolerate wet or even boggy conditions. Propagate from seed or layers.
Ulmus There are some 45 species of elms. Most are trees, some of them very large, though a few are shrubs. Although most are deciduous and very hardy, a few are semi-evergreen and not so tough. They are spread over the northern temperate zones and even extend into the subtropics. Although elms are a diverse lot they tend to share similar characteristics and are fairly easily recognizable. They are generally round-headed trees with bark that is often furrowed or fissured though seldom corky, except on the young shoots. The leaves are usually elliptical with conspicuous veins and serrated edges. The flowers are inconspicuous but the papery winged fruits (samaras) that follow can be showy and may occasionally be mistaken for flowers. CULTIVATION: In the main, elms are tough plants that adapt well to cultivation, growing successfully in a range of soils provided the drainage is good. However, in some areas populations have been decimated by Dutch elm disease, a fungal infection carried by small beetles with wood-boring larvae. Growing elms where the disease is present is difficult and almost certain to result in heartache at some stage. In disease-free areas, though, they couldn?t be more straightforward and are among the most stately and interesting of trees. Propagate by seed or grafting.
Zelkova Allied to the elms (Ulmus) but not troubled by Dutch elm disease, the 5 deciduous trees in this genus are found from the Caucasus to Japan. They have simple, pointed, elliptical leaves with conspicuous veins and heavily serrated edges. The foliage often develops attractive gold to russet autumn colors. In some species the bark is an attractive feature, flaking to reveal interesting patterns and colors. The separate male and female flowers are largely inconspicuous, as are the small nut-like fruits. CULTIVATION: Quite frost hardy, these spreading round-headed trees develop a better shape if sheltered from strong winds when young. They also benefit from pruning to encourage a strong single trunk. Plant in deep, fertile, well-drained soil in full sun. Propagate from seed, root cuttings of young potted plants or by grafting.



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