Betulaceae
Encyclopedia
Betulaceae, or the Birch Family, includes six genera of deciduous
nut
-bearing tree
s and shrub
s, including the birch
es, alder
s, hazel
s, hornbeam
s and hop-hornbeams, numbering about 130 species. They are mostly natives of the temperate Northern Hemisphere
, with a few species reaching the Southern Hemisphere
in the Andes
in South America
.
In the past, the family was often divided into two families, Betulaceae (Alnus, Betula) and Corylaceae (the rest); however, recent treatments, including the Angiosperm Phylogeny Group
, have renamed these two groups as subfamilies within the Betulaceae- Betuloideae and Coryloideae.
The closest relatives of the Betulaceae are believed to be the Casuarinaceae
, or the She-Oaks.
period (c. 70 million years ago) in central China. This region at the time would have had a Mediterranean climate
due to the proximity of the Tethys Sea, which covered parts of present-day Tibet
and Xinjiang
into the early Tertiary
period. This point of origin is supported by the fact that all six genera and 52 species are native to this region, many of those being endemic. It is believed that all six modern genera had diverged fully by the Oligocene
, with all genera in the family (with the exception of Ostryopsis
) having a fossil record stretching back at least 20 million years from the present.
The Common Hazel (Corylus avellana
) and the Filbert (Corylus maxima) are important orchard
plants, grown for their edible nuts
.
The other genera include a number of popular ornamental trees
, widely planted in parks and large gardens; several of the birches are particularly valued for their smooth, brightly coloured bark
.
The wood
is generally hard, tough and heavy, hornbeams particularly so; several species were of significant importance in the past where very hard wood capable of withstanding heavy wear was required, such as for cartwheel
s, water wheel
s, cog wheels
, tool
handles, chopping boards and wooden pegs. In most of these uses wood has now been replaced by metal
or other man-made materials.
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...
nut
Nut (fruit)
A nut is a hard-shelled fruit of some plants having an indehiscent seed. While a wide variety of dried seeds and fruits are called nuts in English, only a certain number of them are considered by biologists to be true nuts...
-bearing tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
s and shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
s, including the birch
Birch
Birch is a tree or shrub of the genus Betula , in the family Betulaceae, closely related to the beech/oak family, Fagaceae. The Betula genus contains 30–60 known taxa...
es, alder
Alder
Alder is the common name of a genus of flowering plants belonging to the birch family . The genus comprises about 30 species of monoecious trees and shrubs, few reaching large size, distributed throughout the North Temperate Zone and in the Americas along the Andes southwards to...
s, hazel
Hazel
The hazels are a genus of deciduous trees and large shrubs native to the temperate northern hemisphere. The genus is usually placed in the birch family Betulaceae, though some botanists split the hazels into a separate family Corylaceae.They have simple, rounded leaves with double-serrate margins...
s, hornbeam
Hornbeam
Hornbeams are relatively small hardwood trees in the genus Carpinus . Though some botanists grouped them with the hazels and hop-hornbeams in a segregate family, Corylaceae, modern botanists place the hornbeams in the birch subfamily Coryloideae...
s and hop-hornbeams, numbering about 130 species. They are mostly natives of the temperate Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
, with a few species reaching the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
in the Andes
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...
in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
.
In the past, the family was often divided into two families, Betulaceae (Alnus, Betula) and Corylaceae (the rest); however, recent treatments, including the Angiosperm Phylogeny Group
Angiosperm Phylogeny Group
The Angiosperm Phylogeny Group, or APG, refers to an informal international group of systematic botanists who came together to try to establish a consensus on the taxonomy of flowering plants that would reflect new knowledge about plant relationships discovered through phylogenetic studies., three...
, have renamed these two groups as subfamilies within the Betulaceae- Betuloideae and Coryloideae.
The closest relatives of the Betulaceae are believed to be the Casuarinaceae
Casuarinaceae
Casuarinaceae is a family of dicotyledonous flowering plants placed in the order Fagales, consisting of 3 or 4 genera and approximately 70 species of trees and shrubs native to the Old World tropics , Australia, and the Pacific Islands...
, or the She-Oaks.
Evolutionary history
The Betulaceae are believed to have originated at the end of the CretaceousCretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period (c. 70 million years ago) in central China. This region at the time would have had a Mediterranean climate
Mediterranean climate
A Mediterranean climate is the climate typical of most of the lands in the Mediterranean Basin, and is a particular variety of subtropical climate...
due to the proximity of the Tethys Sea, which covered parts of present-day Tibet
Tibet
Tibet is a plateau region in Asia, north-east of the Himalayas. It is the traditional homeland of the Tibetan people as well as some other ethnic groups such as Monpas, Qiang, and Lhobas, and is now also inhabited by considerable numbers of Han and Hui people...
and Xinjiang
Xinjiang
Xinjiang is an autonomous region of the People's Republic of China. It is the largest Chinese administrative division and spans over 1.6 million km2...
into the early Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
period. This point of origin is supported by the fact that all six genera and 52 species are native to this region, many of those being endemic. It is believed that all six modern genera had diverged fully by the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, with all genera in the family (with the exception of Ostryopsis
Ostryopsis
Ostryopsis is a small genus of two species of deciduous shrubs belonging to the birch family Betulaceae. The species have no common English name, though Hazel-hornbeam has been suggested, reflecting their similarities to the closely related Hazels and Hop-hornbeams.The genus is native in western...
) having a fossil record stretching back at least 20 million years from the present.
Uses
Corylus avellana
Corylus avellana, the Common Hazel, is a species of hazel native to Europe and western Asia, from the British Isles south to Iberia, Greece, Turkey and Cyprus, north to central Scandinavia, and east to the central Ural Mountains, the Caucasus, and northwestern Iran. It is an important component of...
) and the Filbert (Corylus maxima) are important orchard
Orchard
An orchard is an intentional planting of trees or shrubs that is maintained for food production. Orchards comprise fruit or nut-producing trees which are grown for commercial production. Orchards are also sometimes a feature of large gardens, where they serve an aesthetic as well as a productive...
plants, grown for their edible nuts
Nut (fruit)
A nut is a hard-shelled fruit of some plants having an indehiscent seed. While a wide variety of dried seeds and fruits are called nuts in English, only a certain number of them are considered by biologists to be true nuts...
.
The other genera include a number of popular ornamental trees
Ornamental plant
Ornamental plants are plants that are grown for decorative purposes in gardens and landscape design projects, as house plants, for cut flowers and specimen display...
, widely planted in parks and large gardens; several of the birches are particularly valued for their smooth, brightly coloured bark
Bark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...
.
The wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
is generally hard, tough and heavy, hornbeams particularly so; several species were of significant importance in the past where very hard wood capable of withstanding heavy wear was required, such as for cartwheel
Cartwheel
A cartwheel is a part of a cart. It may also mean:*Cartwheel , an acrobatic maneuver*Cartwheel Galaxy*Cart-wheel hat, worn by women*Slang term for a silver dollar coin -See also:...
s, water wheel
Water wheel
A water wheel is a machine for converting the energy of free-flowing or falling water into useful forms of power. A water wheel consists of a large wooden or metal wheel, with a number of blades or buckets arranged on the outside rim forming the driving surface...
s, cog wheels
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
, tool
Tool
A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...
handles, chopping boards and wooden pegs. In most of these uses wood has now been replaced by metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
or other man-made materials.