March 17
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Plant Species of the genus Alnus

Information about this genus
Name: Alnus
Cultivation: CULTIVATION: The various species are easily grown in their appropriate climates. Those from far northern latitudes do not thrive in warm-temperate regions, while some species from Mexico, the lower Himalayas and southern China are frost tender. Sapling growth is often very fast but they mature early and are sometimes not very long lived. Many are able to thrive in soils of low fertility and poor drainage, aided by nitrogen-fixing fungi in the roots. Propagation is normally from seed, which may need stratification over winter and should not be covered, as germination is stimulated by light. Some cultivars require grafting.
Description: Alders (Alnus) are an essentially Northern Hemisphere genus, closely related to the birches (Betula). Of the 25 species only 2 extend across the equator, down the Andean mountain chain through South America. All are deciduous except for these tropical American species, though even they are often only semi-evergreen. In the wild, alders are fast-growing pioneer trees of disturbed ground such as sand or gravel bars of rivers, glacial moraines and landslips; low-lying boggy ground is another common habitat. Their spread is aided by tiny winged seed, carried by the wind in vast numbers. Alders mostly have darker brownish or blackish bark than birches and their leaves are usually larger and slightly thicker; leaf margins vary from smooth and wavy to jaggedly toothed, and the winter buds are slightly sticky and aromatic. The flowers are tiny but arranged in catkins. The male catkins are long and thin, hanging in profuse bunches at the branch ends, while the female catkins are short and barrel-shaped in less conspicuous groups. Most alders produce catkins just before the new leaves appear in spring.

Specie Vernacular Zone
Alnus 3 elliptica 6?10
Alnus 3 spaethii 5?9
Alnus acuminata 9-11
Alnus cordata 9?10
Alnus firma 6-9
Alnus hirsuta 4-8
Alnus maritima 7-10
Alnus nepalensis 9-10
Alnus orientalis 7-10
Alnus rhombifolia 6-9
Alnus rubra 6-9
Alnus tenuifolia 3-9
glutinosa 4-8
incana 3-9
rugosa 3-9
serrulata hazel alder
viridis 4-9

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