Ulmus pumila

Ulmus pumila, the Siberian elm, is a tree native to Central Asia, eastern Siberia, the Russian Far East, Mongolia, Tibet, northern China, India (northern Kashmir) and Korea. It is also known as the Asiatic elm and dwarf elm, but sometimes miscalled the 'Chinese Elm' (Ulmus parvifolia). It is the last tree species encountered in the semi-desert regions of central Asia. Described by Pallas in the 18th century from specimens from Transbaikal, Ulmus pumila has been widely cultivated throughout Asia, North America, Argentina, and southern Europe, becoming naturalized in many places, notably across much of the United States. The Siberian elm is usually a small to medium-sized, often bushy, tree growing to 10–20 m (35–65 ft) tall, with a trunk up to 176 cm (69 1⁄4 in) d.b.h. The leaves are deciduous in cold areas, but semi-evergreen in warmer climates, less than 7 cm (2 3⁄4 in) long and 3 cm (1 1⁄4 in) broad, with an oblique base and a coarsely serrated margin, the colour changing from dark green to yellow in autumn. The perfect, apetalous wind-pollinated flowers bloom for one week in early spring, before the leaves emerge, in tight fascicles (bundles) on last year's branchlets. However, the flowers, emerging in early February, are often damaged by frost, consequently the species was dropped from the Dutch elm breeding programme. Each flower is about 3 mm (1⁄8 in) across and has a green calyx with 4–5 lobes, 4–8 stamens with brownish-red anthers, and a green pistil with a two-lobed style. Unlike most elms, the Siberian elm is able to self-pollinate successfully. The wind-dispersed fruit develops in a tan-colored flat, oval samara (seed with a membraneous wing around it) 1–2 cm (3⁄8–3⁄4 in) long by 1–1.5 cm (3⁄8–5⁄8 in) wide, notched at the outer end. The tree also suckers readily from its roots. The tree is short-lived in temperate climates, rarely reaching more than 60 years of age, but in its native environment may live to between 100 and 150 years. A giant specimen, 45 kilometres (28 mi) southeast of Khanbogt in the south Gobi, with a girth of 5.55 m in 2009 may exceed 250 years (based on average annual ring widths of other U. pumila in the area). The tree has considerable variability in resistance to Dutch elm disease; for example, trees from north-western and north-eastern China exhibit significantly higher tolerance than those from central and southern China. Moreover, it is highly susceptible to damage from many insects and parasites, including the elm leaf beetle Xanthogaleruca luteola, the Asian 'zigzag' sawfly Aproceros leucopoda, Elm Yellows, powdery mildew, cankers, aphids, leaf spot and, in the Netherlands, coral spot fungus Nectria cinnabarina. However, U. pumila is the most resistant of all the elms to verticillium wilt. U. pumila was introduced into Spain as an ornamental, probably during the reign of Philip II (1556–98), and from the 1930s into Italy. In these countries it has naturally hybridized with the Field Elm U. minor (see below). In Italy it was widely used in viniculture, notably in the Po valley, to support the grape vines until the 1950s, when the demands of mechanization made it unsuitable. Three specimens were supplied by the Späth nursery of Berlin to the Royal Botanic Garden Edinburgh in 1902 as U. pumila, in addition to specimens of the narrow-leaved U. pumila cultivar 'Pinnato-ramosa' (see 'Cultivars' below). One was planted in RBGE; the two not planted in the Garden may survive in Edinburgh, as it was the practice of the Garden to distribute trees about the city. Kew Gardens obtained specimens of U. pumila from the Arnold Arboretum in 1908 and, as U. pekinensis, via the Veitch Nurseries in 1910 from William Purdom in northern China. A specimen obtained from Späth and planted in 1914 stood in the Ryston Hall arboretum, Norfolk, in the early 20th century. The popularity of U. pumila in the Great Britain has been almost exclusively as a bonsai subject, and mature trees are largely restricted to arboreta.