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Nomenclature etc. BETULACEAE. Incl. A. rubra Bong. (syn.: A. oregona Nutt., A. rubra var. pinnatisecta Starker); A. incana (L.) Moench. Trade and local names: A. glutinosa: Schwarzerle, Roterle, Gemeine Erle (DE); common alder, black alder (GB); aune (aulne) (FR); ontano nero (IT); elzen (NL); A. incana: Weißerle, Grauerle (DE); A. rubra: Amerikanische Roterle (DE); (western) red alder, Oregon alder (US). Not protected under CITES regulations.
Tree. Geographic distribution: Europe, excl. Mediterranean, Mediterranean incl. N. Africa and Middle East, temperate Asia (A. glutinosa, A. incana), North America (A. rubra).
General. Growth ring boundaries distinct. Heartwood basically brown, red, yellow, white or grey. Sapwood colour similar to heartwood colour. Density 0.38–0.49–0.6 g/cm³. Frequently with pith flecks.
Vessels. Wood diffuse porous. Vessels arranged in no specific pattern, in multiples, commonly in short (2–3 vessels) radial rows and in radial rows of 4 or more. Vessel outline angular. Average tangential vessel diameter 40–60–90 µm. Vessels per square millimetre numerous. Perforation plates scalariform, with 15–26 bars. Intervessel pits opposite or alternate, average diameter (vertical) 5–6 µm. Vessel-ray pits with distinct borders, similar to intervessel pits, restricted to marginal rows. Vessel-ray pits smaller (ca. 3 µm) than intervessel pits.
Tracheids and fibres. Fibres very thin-walled. Average fibre length 300–1010–1650 µm. Fibre pits mainly restricted to radial walls or common in both radial and tangential walls, simple to minutely bordered or distinctly bordered.
Axial parenchyma. Apotracheal axial parenchyma diffuse, or diffuse-in-aggregates. Axial parenchyma as strands. Average number of cells per strand: 4–8.
Rays. Rays 12–18 per tangential mm, exclusively uniseriate or multiseriate. Aggregate rays present. Height of large rays up to 500 µm. Rays composed of a single cell type (homocellular); homocellular ray cells procumbent. Within aggregate rays up to 3-seriate.
Cambial variants. Other cambial variants present (pith flecks).
Mineral inclusions. Crystals not observed. Silica not observed.
Illustrations. • Macroscopic images. transverse (ca. 10x). radial (natural size). • Transverse section. Alnus viridis. • Tangential section. Alnus viridis. • Radial section. Alnus viridis.
The interactive key allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting specified attributes, summaries of attributes within groups of taxa, and geographical distribution.
Cite this publication as: ‘Richter, H.G., and Dallwitz, M.J. 2000 onwards. Commercial timbers: descriptions, illustrations, identification, and information retrieval. In English, French, German, Portuguese, and Spanish. Version: 9th April 2019. delta-intkey.com’.
