Characteristics of the genus “Betula” (Birch)
What is a birch?
Birches are trees or shrubs of the genus Betula in the order of fagales which includes other trees such as oak, beech, alder, etc. Birches grow in the mountains or in northern temperate zones. Birch (Betula pendula) forms large forests in Scandinavian taiga (in latitudes between 50 and 70 degrees north latitude).
The word comes from the Celtic Birch bitumen, which was the name that people gave to the birch. Some researchers say that the name could come from Sanskrit bhurga, meaning “tree to write” by the fact that the bark of this tree was used as a paper before inventing it .
What are birches like?
The birch tree presents medium trees or specimens of a bushy form. The latter are more common in high places or in very cold areas. The leaves are simple, alternate and petiolated; they are about 3 to 8 cm and are generally “dentata” (toothed), although there are species with lobes. Many of them are diamond-shaped and often pointed.
The branches and trunks usually have a more or less clear gray bark, often split into layers as the tree gets older and the lower crust reveals a different color depending on the species. The color of the bark is one of the features that differentiate the various species of birch. Most of them lose this “peel” because underneath this surface crust appears another, the final one. It is characteristic to notice the presence of pores called lenticels on the surface of the birch bark, which allow the upper crust to breathe and make way for the gases to the lower crust.
The bark is rich in oils and components that make it very resistant to the environmental aggressions. This is one of the reasons why this tree can withstand the cold and wind of the northern latitudes.
The birches are trees with separate male and female flowers on the same tree (monoecious trees.) The flowers develop in a plant formations called catkins, which may be erect or hanging, and are formed by grouping a series of overlapping bracts. The male flowers have 2 to 4 filaments and are grouped in trios in the axils of each bract. The male catkins hang at maturity. The female flowers appear in groups of 2 to 3 in the axils of the bracts. Each has an ovary with one egg and two styles. The female catkins are pendent. The fruits have the shape of winged achenes, which encourages them to seed dispersal by wind.
Photo of tools (axes, saws, plows, etc.) made of birch wood as shown at de Vos Museum (Norway)
Uses of birches
The birches are trees that have many uses in certain areas of our planet. The birch bark, for its oil, which is practically imperishable is used as insulating material. Many houses in Scandinavia use this crust to build waterproof roofs.
To do this, they place a layer of bark under a roof, like a box that has been filled with peat and on which grass is planted. The birch bark layer acts as an insulator in the peat that is always wet or damp as a result of the constant rain and below the wooden roof protects.
This ability to resist humidity and harsh conditions has also been used in the manufacture of utensils and tools, clogs, baskets, wooden boxes, plates, etc. Canadian and American Indians took advantage of birch bark to line their canoes.
This inner layer waterproofing means of transport and ensure that no sink. The branches and young leaves are dried and used as winter fodder for animals.
Birch is Finland’s national tree. It is traditional to show a girl reclining on a birch as a Finnish emblem. It is also usual in this country to offer the bride a ring of birch bark before giving the final ring. The reason for this devotion to this tree lies in the fact that this tree is one of the most common in this country and probably the one that has been used throughout history.
Even today it is considered that one in ten households in this country used its wood for heating during the winter.
Birch wood is the primary fuel for a lot of northern people. In the picture you can see how the wood is cut and prepared for burning in homes and withstand the harsh winter. For its richness in oil it is a type of wood that lights well and provides plenty of heat.
In the timber industry, birch has played an important role in the manufacture of plywood. Currently, its greatest importance lies in the manufacture of paper pulp.
With birch bark, betulin-rich and betulinic acid, is gets as oils that are used in the automotive, paints and other industrial applications. The pharmaceutical industry uses birch tar to produce medicines in the form of ointments or liniments with which treat rheumatic pain or pain from bruises. Birch is very rich in sugars.
Xylose is extracted from birch wood and it is used in the production of xylitol as a sweetener for in some candy and chewing gum, since it does not produce tooth decay. Its use is widespread in northern Europe, especially in Finland. It is also included in the composition of manufactured foods for diabetics because it does not require insulin for the body to metabolize.
Edible and curative properties of birch
The inner bark of the birch is edible. The inhabitants of northern countries have consumed it in times of famine, when there was no other more appetizing food. It can be eaten cooked or dried, and ground. For its quantity of starch it has been used as flour mixed with cereal flour such as wheat, barley or oats.
Birch sap, very rich in sugars, is used fresh with therapeutic properties as one of the best resources as a tonic, to treat kidney stones and to dissolve sand in the kidney (For more information on this subject in the Under “Birch sap” in the listing above)
The birch leaves are used primarily in natural medicine for the preparation of herbal teas. They contain a higher percentage of saponins that the crust and are rich in tannins, resins and bitter principles. This makes them an essential ally in the treatment of uric acid, edema, cholesterol and hair loss (See more information about this topic in the section “Medicinal properties of birch” in the listing above).
MAIN SPECIES OF GENUS BETULA (BIRCHES)
Among the 60 species of the genus Betula, we could emphasize the following:
Main species of birch in Europe and Asia
Silver Birch: (Betula pendula Roth = Betula alba = Betula verrucosa Ehrh) deciduous tree or shrub in the family Betulaceae up to 25 m. tall with drooping branches. Trunks are erect, with white or gray bark with reddish tones in the young specimens, wrinkled and dark at the base of the stem which is usually easily split into strips. Young glabrous twigs with the presence of rough warts and glands that produce white resin. Ovoid, glabrous and doubly toothed long teeth leaves alternating with other shorter, up to 6 cm. Flowers gathered in catkins, the male ones erect in youth and hanging in maturity, the female ones upright. Pendulous Fruit, cylindrical, up to 4 cm long that open at maturity expelling its winged seeds.
Photo of silver birch (Betula pendula)
It is a tree from southwest Asia (Turkey and Caucasus) which can be found wild in most of the mountains up to 3000 meters. It is practically in most forests and heaths throughout Europe, along rivers and streams. It appears regularly throughout Europe sharing habitat with other trees in temperate mixed forests. Being a tree that lets light through, it can live with other trees such as willows, oaks, ash, lindens, maples. Many shrubs and plants also grow beneath it, such as holly or hazel.
In more continental forests, the rigors of cold are placing this species as dominant over the other deciduous trees. However, it is in most northern areas of northern Europe where this species reaches its peak.
It forms large forests in the Scandinavian boreal forest or taiga located between 50 and 70 degrees North Latitude. These are transitional forests in which this birch is a colonizing species (pioneer species) that takes advantage of the gaps that remain after the fires. Being a fast growing tree and a lover of light, it is able to reforest in a period of 60 years the land that should be occupied by Scots pine (Pinus silvestris) that are replacing the birch forests. In turn, the pines are replaced by spruce (Picea abies) which form the climax vegetation, ie the final and stable vegetation that occupies this habitat. It is estimated that the whole evolutionary process in the taiga of Scandinavia can last about 500 years.
It grows from a common form in Canada. It prefers limestone and moist soils.
Downy birch (Betula pubescens Ehrh) deciduous tree or shrub in the family Betulaceae up to 30 m. high. White or gray bark, erect trunks. Unlike the species Betula pendula, the crust is not reddish or wrinkled or dark at the base of the stem and therefore it is not usually split into strips. Young twigs are pubescent clear and do not hang; they can have a presence or absence of warts and no resinous glands. Ovate and acuminate leaves up to 5 cm long, covered, as the bark,of a white waxy covered with silvery hairs on the nerves of the back, not doubly toothed as in B. pendula and generally more rounded, with hairy petioles. Flowers gathered in catkins, the male erect in youth and hanging in maturity, the female upright. Pendulous and cylindrical fruit, up to 4 cm long, that open at maturity expelling its winged seeds.
Photo of downy birch (Betula pubescens) occupying the highlands of Norway
Species from Asia at its height on heaths or swamps, especially in northern Europe, being very common in Norway, Sweden, Finland, Iceland and northern Asia. It tends to prefer more humid areas of siliceous nature than the pendulum birch (Betula pendula)
In the northernmost regions, it appears with the variety Betula pubescens subsp. = Betula pubescens tortuosa subsp. czerepanovii, called arctic white birch, which can be found further north. (Some authors do not differentiate between the two subspecies). In peaty and poor soils in Northern Europe and in the high mountains of south it produces large forests. The northern forests are more sparse, with specimens of smaller size until its complete disappearance when they are replaced by dwarf birch (Betula nana L.) which has a shape lying shrub and not reaching more than 100 cm in height.
In places of less extreme weather it can cross with the pendulum birch, producing hybrids that share common characteristics.
Hybrid species Betula pendula and Betula pubescens: The two species often hybridize with ease before producing species that share common characteristics and are sometimes difficult to distinguish. This is especially true in northern Europe.
Dwarf Birch or Bog Birch (Betula nana) has a low shrub scrub size that do not exceed more than 100 cm in height. Stolon presents dark red pubescent twigs. Small leaves, up to 1.5 cm, rounded, with coarse teeth and prominent, beautiful when young, glabrous as they mature.
The dwarf birch is the most prominent shrub in the tundra, being very common to find it in Scandinavia and Central Europe in swamps and bogs to 2000 meters. It can also be found very rarely in some mountains of Scotland.
Photo of dwarf birch (Betula nana) crawling on a stone in a bog in Finland.
Himalayan Birch (Betula utilis) is a tree from the Himalayas that heights more than 18 meters. It has pale gray trunks that are peeled off easily and leaves up to 8 cm with a beam of dark green and a much clearer back part.
Japanese white birch (Betula plathyphylla) is a species that can be found in eastern and western Siberia and northern China, Korea and Japan. It has a white crust without spots.
Chinese red birch (Betula albosinensis) birch species native to the west of China, which can reach 12 meters high. Highlights of the lower crust color that appears to peel the outer layer of gray color and offers a beautiful copper colored. Its leaves are oblong, have very prominent teeth and may reach 8 cm in length.
Alaska birch (Betula neoalaskana): birch that grows in the interior areas of Alaska and Canada. Reaches 12 m in height. Stems with a brownish-white bark.
Main American species of birch
Black birch or sweet birch (Betula lenta) American birch species to 23 m in height. Trunk bark of bright color, reddish brown to black.
Gray birch (Betula populifolia) North American species that grows in the colder areas where other species of birch cannot grow. Leaves of up to 8 cm long, very acuminate and stems of a pale gray color.
Yellow birch (Betula alleghaniensis) Birch of the highest port in the eastern United States and Canada. It can reach 30 meters high. The bark is of a creamy yellow color, even gold and breaks easily into strips. It is planted to be used commercially, because of the value of its timber and the high proportion of oil. Very long leaves with very jagged edges.
|Scientific overview of Betula species and varieties|
|Betula alleghaniensis Britt.
Betula alleghaniensis Britt. var. alleghaniensis
Betula alleghaniensis Britt. var. macrolepis (Fern.) Brayshaw
Betula ×alpestris Fr. P
Betula ×alpestris Fr. var. ×sukaczewii (Soczava) Govaerts P
Betula borealis Spach
Betula ×caerulea Blanch.
Betula ×caerulea Blanch. var. caerulea
Betula ×caerulea Blanch. var. grandis Blanch.
Betula ×dugleana Lepage P
Betula ×eastwoodiae Sarg. P
Betula glandulosa Michx.
Betula ×hornei Butler P
Betula ×jackii Schneid. P
Betula lenta L.
Betula maximowicziana Regel
Betula minor (Tuckerman) Fern.
Betula murrayana Barnes & Dancik
Betula nana L.
Subspecies Betula nana L. ssp. exilis (Sukatschev) Hultén P
Subspecies Betula nana L. ssp. perfiljevii (V.N. Vassil) A.& D. Löve P
Betula neoalaskana Sarg.
Betula nigra L.
Betula occidentalis Hook
|Betula papyrifera Marsh
Betula papyrifera Marsh. var. cordifolia (Regel) Fern.
Betula papyrifera Marsh. var. kenaica (W.H. Evans) A. Henry
Betula papyrifera Marsh. var. papyrifera
Betula pendula Roth
Betula pendula Roth var. dalecarlica Schneid
Betula platyphylla Sukatschev
Betula platyphylla Sukatschev var. japonica (Miq.)
Betula platyphylla Sukatschev var. kamtschatica (Regel)
Betula platyphylla Sukatschev var. platyphylla
Betula populifolia Marsh
Betula pubescens Ehrh
Betula pubescens Ehrh. var. pubescens
Betula pumila L.
Betula pumila L. var. glabra Regel
Betula pumila L. var. glandulifera Regel
Betula pumila L. var. pumila
Betula pumila L. var. renifolia Fern
Betula ×purpusii Schneid. P
Betula ×sandbergii Britt. P
Betula ×sargentii Dugle P
Betula szechuanica (Schneid.) C.A. Jansson
Betula uber (Ashe) Fern
Betula ×utahensis Britt
Betula ×winteri Dugle P