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Ulmus pumila L.
Common name: olmo de Siberia (Siberian elm).
Deciduous tree of up to 15 m height and 0.5 m diameter.
The twigs are thin (~1.5 mm) and completely glabrous. Buds are small, brownish-dark, some ovoid and acute (the ones which will produce the branch shoots) and others are globose (the ones to become inflorescences). All of them have imbricate scales, often covered by a white, dense hairy layer in their upper end and the scale edges.
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Leaves are alternate, more or less arranged in two opposite rows (distichous). They are simple, with a short petiole (<12 mm) and a long blade (5-7 cm), elliptical or elliptical-lanceolate. With a lot of secondary veins (6-10 pairs), with a less asymmetrical base (the differences can hardly be seen), they have a doubly serrated margin and acute apex.
The flowers are gathered in round bundles attached to the branchlets. They are bisexual, formed by an external, membranaceous, short tubular piece ended in 4-8 deep lobes; the male part, with 3-8 stamens with exserted anthers, reddish when mature; and the female part with one pistil of rounded, very compressed and glabrous ovary ended by two divergent, whitish, very papillose stigmata.
The fruits form glomerules beside the twigs, initially green and afterwards, during full maturity, brownish-yellow. They are samaras of short stalks, round-shaped or slightly obocate, glabrous, with a notch in the upper end and a centered seed.
Biology and phenology
Sexual maturity is reached early, usually about 4 or 5 years. Soon flowering occurs in abundance. It occurs in late winter, with the first sunny days that announce the change of season. It is the earliest among our elms.
There is wind pollination (anemogamy). Once achieved, fertilization arrives promptly, thus involving the maturity of fruits at the beginning of the leaves sprout. The production is regular and the dissemination by wind occurs in a few days.
Distribution, ecology and past uses
Ulmus pumila comes from Eastern Asia. It has been plentifully used along linear plantations in streets and, in a lesser extent, roadways. In the peninsular Spain, this species often occurs as feral, but it is not included in the Atlas of Allochtone Invasive Plants in Spain. It occurs frequently in peri-urban areas and occasionally planted in river and lake banks, recreation sites in forests etc. The species requires water during the summer season, but the demand is lower than the one of the Spanish elms. It grows either on calcareous or siliceous soils.