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Ulmus laevis Pall.
Common name: its common name is unknown in Spain, but it could have been ‘negrillo’
It is as tall as Ulmus minor, also reaching heights of up to 30 m. Its trunk can reach 1,5 m diameter.
Leaves with a short petiole (~ 12 mm), 10-20 pairs of lateral veins. This species shows the highest degree of asymmetry at the leaf blade base (13 mm of difference). The upper side is finely pubescent and smooth; the back side is slightly tomentous.
Flowers grow at the end of long, nodding stalks (up to 25 mm), gathered in clusters, which become conspicuous, as hanging bundles, when the tree has not flushed its leaves yet. They are bisexual or male, with an external piece with several asymmetric lobes, 5-9 stamens and a compressed pistil ended by two small divergent, feathery, whitish stigmata.
Fruits are subsequently hanging from long pedicels. They are small samaras, 1 cm long, with ciliate margin, the best characteristic for distinguish this species from the former one, the common elm. Seeds are also different, as their location is in the samara lower half.
Biology and phenology
The flowering period occurs in the late winter before leaves sprouting, but the bloom is later than Ulmus minor’s. Flowers are pollinated by the wind, but some authors give importance to insects as pollinators.
Fruits are mature in late spring, after Ulmus minor’s ones, but, similarly, after de full development of leaves. The fruit production is irregular (it is a masting species).
Distribution and ecology
It is a colonizing species, showing a dispersal strategy similar to other Ulmus.
In the Iberian Peninsula, Ulmus laevis grows between 300 and 1000 m above sea level. It is hydrophile, but unlike Ulmus minor, the interpretation of its habitat is limited because of the scarce current populations. Due to its higher water requirements, its natural lands would be riverbanks and depressions, being less frequent on floodplains or watercourses were the phreatic level is lower in summer. In the rest of Europe, this species is considered as tolerant to carbonated soils, but the Spanish populations of Ulmus laevis seem to be calcifuge, an unusual pattern also present in some other species.
This taxon has been known as Ulmus pedunculata as well.