September 26
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Plant Genus of the family Betulaceae

Genus Description Cultivation
Alnus 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. 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.
Betula This genus in the family of Betulaceae consists of about 60 deciduous species occurring in mountains, heath, moors and woodland throughout the temperate and arctic zones of the Northern Hemisphere. Depending on the species these can be small shrubs or tall trees. Tree trunks are often marked in shades of white-pink to a glossy brown and in many species the outer layer of bark peels off in thin paper-like strips. Historically, many countries have used these strips as material to write on. Ancient Buddhist literature is one such example. The wood from many species is used for timber for the furniture trade, as plywood or wood pulp. Sap and leaves are used medicinally, as food or drink, and as dye-stuff. The young tree and small twigs are often red-brown with pendulous male catkins and erect female catkins carried on the same tree. The catkins are formed the previous autumn and overwinter on the tree to blossom in early spring. Birch foliage is mid to dark green, arranged alternately on branches, and in most species ovate in shape and with indented margins. Birches are good ornamental trees and are important to the nursery trade in temperate areas. CULTIVATION: Birches are among the hardiest trees. They can stand extreme cold and exposure to wind. Birches do best in well-drained fertile soil, with some moisture, in full sun or light shade. Take softwood cuttings in summer or half-hardened cuttings in autumn: mist propagation is advisable, or graft cultivars in winter. Seed from birches grown in gardens usually does not come true. Birches are susceptible to several fungi including Armillaria melea and Piptoporus betulinus; the latter, specific to the birch family, will destroy the tree.
Carpinus This genus contains about 35 deciduous trees and shrubs that are found throughout the temperate regions of the Northern Hemisphere. Commonly known as hornbeams, they are appealing trees at all times of year. The leaves have prominent parallel veining and color well in autumn. In spring pendulous yellow male catkins and separate female catkins, which are erect at first, are borne. The fruiting clusters in autumn are surrounded by leafy bracts and in winter an attractive branch pattern is revealed. CULTIVATION: Hornbeams will grow in most soils and are suitable for parks and specimen plantings.Carpinus betulus is popular for pleaching and hedging. Species are propagated from seed sown in autumn and cultivars are grafted.
Corylus Variously known as filberts, hazelnuts, cobnuts and cobs, there are about 15 species of deciduous suckering shrubs and trees in this genus, of which some are garden grown. The flowers, both the long flouncing male catkins (also known as lambs? tails) and the almost unnoticeable female flowers, appear on last year?s bare wood with the same plant carrying both sexes. The decorative catkins are usually visible by late winter and fluff out in spring when the female flowers appear. The distinctively husked edible nuts ripen in autumn. The plants have a long history in cultivation, and over the centuries have been put to a variety of uses including thatching. CULTIVATION: They are easily grown and generously fruitful when grown on rich moist soils and placed in full sun or part-shade. Propagate from detached suckers, mounding up soil beforehand if necessary to promote root growth. Early summer softwood cuttings are also used, treated with hormone powder. Seeds require cold stratification for about 3 months for germination.
Ostrya This genus contains about 10 species of deciduous trees related to Betulus and Carpinus. They grow throughout the Northern Hemisphere temperate regions in open woodland. The alternate leaves have conspicuous veining and toothed edges, and are often hairy. The male catkins resemble the flowers of hornbeams (Carpinus). The female flowers, on the same tree, develop into catkins that look much like those of hops (Humulus), with overlapping bracts. CULTIVATION: These slow-growing trees are not common in cultivation. They prefer well-drained fertile soil in either sun or shade, and make good specimen trees. Propagate in spring from fresh seed in pots protected from frosts. Seed which has dried out must be stratified to break dormancy. Graft cultivars onto Carpinus betulus rootstocks in the colder months.

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