Acacia

An acacia in the desert of Makhtesh Gadol, Negev, Israel.

Acacia drepanolobium.

Acacia sp.

Acacia is a genus of trees in the Fabaceae family. Many leguminous trees of this genus and also of other genera are known by the common name "acacia".

There are some 1,400 accepted species, of the more than 3,000 described in the world. Some 970 belong to the genus Acacia stricto sensu, of which 950 come from Australia.

Description

They are trees or shrubs, thorny or unarmed, deciduous or evergreen, with alternate, unarmed or thorny branches. They have pulvinulate leaves, stipulated or not, petiolate, uni or bi-paripinnate, or reduced to phyllodes; the stipules are free from each other, fleeting or highly developed and transformed into spines; the rachis frequently shows glands, more or less annular, located at the base of the pinnae and the leaflets have entire margins.

The inflorescences are organized in cylindrical or globose glomeruli, with numerous flowers, frequently grouped in complex racemose inflorescences (conflorescences). The flowers are actinomorphic, without hypanthia, hermaphroditic or unisexual, and yellow in color. The sepals, 4-5 in number, are welded at the base and more or less obtuse. The 4-5 petals are longer than the sepals, acute, welded together at the base to form a tube. The androecium is made up of numerous stamens, free from each other and with very long, cylindrical, glabrous staminal filaments; the anthers are ovoid, with or without glands. The ovary is seated or pedunculated, glabrous or pubescent, with several uniseriate or multiserial seminal rudiments and a more or less cylindrical style with moist, funneled stigma.

The fruit, seated or pedicled, is dry, dehiscent or indehiscent, flattened to subcylindrical, generally with several more or less discoidal seeds, frequently with a persistent, well-developed and somewhat fleshy funicle (aril). It measures from 7 to 10 meters high.

Distribution and habitat

A widespread genus in tropical and subtropical regions of the world. The greatest diversity of species is found in Africa and Australia. In general, the species of Oceania are represented as the dominant part of the vegetation, especially in the arid and semi-arid zones.

History

Among the ancients, the acacia was considered a wonderful plant, for its healing properties and was considered extremely effective in warding off bad luck. In Egypt, this tree was well known and its natives used it for the construction of boats, statues and furniture. Among the Hebrews, it is cited as setim wood and according to the holy books, in the construction of the tabernacle the only wood that was used was Acacia seyal.

Reactive species

Some species of acacias have a defense system that some biologists consider to be unique in the plant kingdom. In conglomerates where each individual is in close contact with another, if this is approached by a predator of its foliage, the plant reacts chemically releasing substances that are airborne and reach the other plants "giving the alarm"; Immediately, the rest of the specimens in the conglomerate begin to secrete a toxic substance in their leaves —they change color, darkening— that is harmful on contact and ingestion and even deadly for the animal predator (which can be, for example, a large mammal such as a giraffe, although there have been cases of pet poisoning).

This reaction is temporary, even so, the species of acacia must be appropriately selected in the field of gardening, in order to avoid these effects on animals and people.

Taxonomy

The genus was described by Gerrit Smith Miller and published in The Gardeners Dictionary, Abridged, Fourth Edition, vol. 1 in 1754. The type species is Acacia scorpioides (L.) W. Wight.

Etymology

• Acacia: generic name derived from the Greek ακακκααakakia), which was awarded by the Greek botanist Pedanius Dioscorides (90-40 BC) for the medicinal tree A. nilotica in his book Medical (About the medicinal matter). The name derives from the Greek word, ακις (akis ‘spinas’). The thorns are found in the species of African acacias, as Australians usually lack them.

Taxonomic classification

Several recent cladistic analyzes have shown that the genus Acacia is not monophyletic. While the subgenus Acacia (now Vachellia) and the subgenus Phyllodineae are monophyletic, the subgenus Aculeiferum is not.. This subgenus is made up of three clades. Therefore, the genus Acacia does not remain as a single entity, rather the genus is divided into five other different genera: Acacia s.s.p., Vachellia, Senegalia, Acaciella and Mariosousa. The new type species of Acacia has become Acacia penninervis .

The genus was previously typed as the African species Acacia scorpioides (L.) W.F. Wright, a synonym of Acacia nilotica (L.) Delile. Under the original typification, the name Acacia would remain with the group of species currently recognized with the genus Vachellia. Orchard and Maslin proposed a retyping of the genus Acacia with the species Acacia penninervis Sieber ex DC., an Australian species that is a member of the larger clade within Acacia, a mainly Australian group formerly recognized as Acacia subgenus Phyllodinae, on the basis that this results in the least changes in nomenclature. Although this proposal was strongly rejected by some authors, it was accepted on July 16, 2005 by the XVII International Botanical Congress in Vienna, Austria and confirmed in Melbourne in 2011. Consequently, the name Acacia is conserved for 948 Australian species, 7 in the Pacific islands, 1 or 2 in Madagascar and 10 in tropical Asia. Those outside Australia are divided into the genera Acaciella, Mariosousa, Senegalia, and Vachellia. However, many references to these trees in guidebooks and botanical books still retain the traditional names of Acacia even though they are not Australian, and are considered "pre-break" names. This extra-Australian group is native to South America, the West Indies and Africa.

Accepted species

The most cultivated species are:

• Armata space, used for hedges, foliolos of dark green colour, with thorns, yellow solitary flowers. No more than four meters.
• Dance gamefast growth, even short-lived. Hanging branches, cluster inflorescences. No more than six meters.
• Acacia dealbata, widely cultivated as an ornamental plant in the temperate regions of the world, grows up to thirty meters high.
• Longifolia, fast growth, up to seven meters, very tolerant to lime. Coriaceous philosophies.
• Acacia mucronata, very resistant, very narrow edges.
• Verticillata space, dense shrub, up to six meters, with pungent phylodes, in verticils.
• Farnesian space, smaller shrub, common in dry forest areas of Central America.

False acacias, and/or similar species

Among the similar species called "acacias", the so-called "false acacias" stand out, made up of Gleditsia triacanthos, Robinia pseudoacacia and Sophora japonica; which are planted in many cities around the world to decorate streets and parks.

Although less similar, they are also often confused with carob trees (Ceratonia and Prosopis), a product of their pods and, to a lesser extent, their foliage.