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Plantwise Technical Factsheet

European field elm (Ulmus minor)

Description
Habit

A relatively fast-growing erect tree with ascending and spreading branches, dense foliage, forming a conical or globular crown with one or more domed tops. Full-grown trees often present long pendulous branches with terminal twigs curled upward at the tips. The twigs are usually slender, glabrous (often tomentose in the southern part of its range). Morphological features exhibit extreme variation within this wide-range species, particularly in the Mediterranean area. Thus, the shape of the canopy ranges from that of an umbrella or a ball to narrow and slender forms (note also the regular cone of variety sarniensis and the straight trunk and narrow silhouette of variety cornubiensis).

Size

It may grow up to 30 and 40 m in height depending on soil water and nutrient supply; corresponding d.b.h. may reach 150 to 200 cm.

Stem form

The bole may be short or extend up to half the total tree height. In the variety cornubiensis it is typically very straight and does not branch off.

Important characteristics

A characteristic that clearly distinguishes U. minor sensu latissimo Richens from the other two European elms (U. glabra and U. laevis) is the presence of root suckers. The bark, smooth in 1-2 year old twigs, soon becomes rough and fissured into vertical ridges on the bole and big branches. There is variation in the kind of fissuring. The early fissuring of bark distinguishes field elm from U. glabra. Vigorous twigs and branchlets may present corky wings which depend greatly on environmental conditions (Grudzinskaja, 1956). The root system is well-developed and extends as deep as 150-160 cm even in compact soil (Namvar and Spethmann, 1985).

Foliage

The bilateral asymmetry and the double tooted margin of the leaf distinguish the genus Ulmus from almost all other trees. The leaf also provides the most useful taxonomic characters for discrimination among elms. Because of the notable variation of leaf shape between saplings and adult trees and even on the same tree, the second and third leaves from the apex of the short shoot (typically bearing 5 leaves) should be considered for diagnostic purposes (Richens, 1983). Leaf shape is variable from obovate acute to near orbicular, 5-10 cm long, 2.5-5 cm width, with 9-12 pairs of lateral veins frequently forked near the margin. Melville (1946) suggests the existence of a geographical cline for increasing leaf breadth from north to south. Hairiness of leaf blade, leaf stalk and shoot is variable, and likewise tends to be more frequent proceeding southwards towards the Mediterranean. However, the taxonomic value of this morphological characteristic is questioned by Richens (1983). The species/variety canescens is characterized by dense hairiness of the lower surface of leaf, while the leaf of U. minor var. minor is glabrous. The petiole is relatively long (9-15 mm), easily distinguished from the shorter petioles of U. glabra and U. laevis.

Inflorescences, flowers and fruits

The very small (3 cm long), bisexual flowers with a very short stalk are joined in clusters of 15-35 individuals. The perianth is cut in 4-6 ciliate lobes, with 4 stamens and an ovary presenting a prominent bifid gland-covered stigma. The pollen, which is allergenic, may be wind-born for distances up to 1500 km (Richens, 1983) - despite this, elms are actively visited by bees. Maturing of the male and female part of the flower is non-simultaneous (for more information, see Mittempergher and Porta, 1991). All elm species are diploid (2n = 28) with the exception of U. americana which is tetraploid. Self-incompatibility is very high.

The fruit is a samara, with a short peduncle, broadly to narrowly obovate, smooth, 13-23 mm long, 8-13 mm wide with seed located in the centre about 1/3 of the length from the apex, often coloured red over the seed. (By comparison, U. glabra seed is located in the centre of the samara, and U. laevis has long pedunculate flowers and ciliate samaras.)

Phenology

As with most elm species, field elm is a deciduous tree with leaves turning yellow before falling in autumn. All European elms flower at the end of the winter (February-March) before the leaves appear. The seed ripens a couple of months after pollination and germinates immediately. Germination is epigeal and gives rise to a seedling with a reddish hypocotyl, obovate cotyledons and decussate primary leaves showing a simple dentate margin.
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