Adansonia
Adansonia digitata in Tanzania
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Malvales
Family:	Malvaceae
Subfamily:	Bombacoideae
Genus:	Adansonia L.[1]
Species
See Species section

Adansonia is a genus made up of eight species of medium to large deciduous trees known as baobabs . Previously classified within the family Bombacaceae, they are now placed in the Malvaceae. They are native to Madagascar, mainland Africa^[2] and Australia.^[3] Trees have also been introduced to other regions such as Asia.^[2][4][5] The generic name honours Michel Adanson, the French naturalist and explorer who described Adansonia digitata.^[6] The baobab is also known as the "upside down tree", a name that originates from several myths.^[7] They are among the most long-lived of vascular plants^[8] and have large flowers that are reproductive for a maximum of 15 hours.^[9] The flowers open around dusk; opening so quickly that movement can be detected by the naked eye and are faded by the next morning.^[9] The fruits are large, oval to round and berry-like and hold kidney-shaped seeds in a dry, pulpy matrix.

In the early 21st century, baobabs in southern Africa began to die off rapidly from a cause yet to be determined. Scientists believe it is unlikely that disease or pests were able to kill many trees so rapidly, and some speculated that the die-off was a result of dehydration from global warming.^[10][11]

Description

General

Baobabs are long-lived deciduous, small to large trees with broad trunks and compact crowns. Young trees usually have slender, tapering trunks, often with a swollen base. The trunk is made of fibrous wood arranged in concentric rings. Tree diameter fluctuates with rainfall so it is thought that water may be stored in the trunk.^[9] Baobab trees have two types of shoots - long, green vegetative ones, and stout, woody reproductive ones. Adansonia gregorii is generally the smallest of the baobabs, rarely getting to over 10 m tall and often with multiple trunks.^[9] Both A. rubrostipa and A. madagascariensis are small to large trees, from 5 to 20 m (16 to 66 ft) tall.^[9] The other baobabs grow from 25 to 30 m (80 to 100 ft) tall, with 2 to 3 m (7 to 10 ft) diameter trunks. A. digitata however often have massive single or multiple trunks of up to 10 m (33 ft) diameter.^[9]

Leaves

Leaves are palmately compound in mature trees, but seedlings and regenerating shoots may have simple leaves. The transition to compound leaves comes with age and may be gradual. Leaflets may have toothed or smooth edges and may be hairless or have simple to clumped hairs. Baobabs have stipules at the base of the leaves, but the stipules are soon shed in most species.^[9]

Flowers

Flowers are born near the tips of reproductive shoots, in the axils of the leaves. There is usually only a singe flower in an axil, but sometimes flowers occur in pairs. They are large, showy and strongly scented. They only open near dusk. Opening is rapid and movement of the flower parts is fast enough to be visible. Most Adansonia species are pollinated by bats.^[12] Flowers may remain attached to the trees for several days, but the reproductive phase is very short, with pollen shed during the first night and stigmas shriveled by the morning. The flower is made up of an outer 5-lobed calyx, and an inner ring of petals set around a fused tube of stamens.^[9]The calyx is usually green (brown in A. grandidieri Baill.) ^[9] and made up of 5 lobes that in bud are joined almost to the tip. As the flower opens, the calyx lobes split apart and become coiled or bent back (reflexed) at the base of the flower. Sometimes the lobes do not separate cleanly, distorting the shape of the flower as they bend back. The calyx lobes remain fused at the base, leaving a feature (calyx tube) that has nectar-producing tissue and that is cup-shaped, flat or tubular; the form of the calyx tube varies with species.^[9] The flowers have a central tube (staminal tube) made up of fused stalks of stamens (filaments), with unfused filaments above. A densely hairy ovary is enclosed in the staminal tube, and a long style tipped with a stigma emerges from the filaments. Petals are set near the base of the staminal tube and are variable in shape and colour. The flowers, when fresh, may be white, cream, bright yellow or dark red, but fade quickly, often turning reddish when dried.^[9]

Fruit

The fruit of the baobabs is one of their distinguishing features. It is large, oval to round, and berry-like in most species (usually less than 10 centimetres (3.9 in) long in A. madagascariensis.^[9]). It has a dry, hard outer shell of variable thickness. In most species, the shell is indehiscent (does not break open easily). A. gibbosa is the only species with fruits that crack while still on the tree, so then tend to break open upon landing on the ground. Inside the outer shell, kidney-shaped seeds are set in a dry pulp.^[9]

Species

Adansonia grandidieri, Madagascar

Adansonia digitata, Niger

As of July 2020^[update], there were considered to be eight species of Adansonia, with six endemic to Madagascar, one native to mainland Africa and the Arabian Peninsula, and one native to Australia. The mainland African species (Adansonia digitata) also occurs on Madagascar, but it is not a native of that island. Baobabs were introduced in ancient times to south Asia and during the colonial era to the Caribbean. They are also present in the island nation of Cape Verde.^[7] A ninth species was described in 2012 (Adansonia kilima Pettigrew, et al.)^[13] but is no longer recognized as a distinct species.^[14] The African and Australian baobabs are almost identical despite having separated more than 100 million years ago, probably getting to Australia from Africa by oceanic dispersal.^[15]

Habitat

The Malagasy species are important components of the Madagascar dry deciduous forests. Within that biome, Adansonia madagascariensis and A. rubrostipa occur specifically in the Anjajavy Forest, sometimes growing out of the tsingy limestone itself. A. digitata has been called "a defining icon of African bushland".^[20] The tree also grows wild in Sudan in the regions of Darfur and the state of Kordofan . The locals call it "Gongolaze" and use its fruits as food and medicine and use the tree trunks as reservoirs to save water.

Ecology

Baobabs store water in the trunk (up to 120,000 litres or 32,000 US gallons) to endure harsh drought conditions.^[21] All occur in seasonally arid areas, and are deciduous, shedding their leaves during the dry season. Across Africa, the oldest and largest baobabs began to die in the early 21st century, likely from a combination of drought and rising temperatures.^[10] The trees appear to become parched, then become dehydrated and unable to support their massive trunks.^[11]

Baobabs are important as nest sites for birds, in particular the mottled spinetail^[22] and four species of weaver.^[23]

Notable trees

"Grandmother" Fony baobab

Radiocarbon dating has provided data on a few individuals of A. digitata. The Panke baobab in Zimbabwe was some 2,450 years old when it died in 2011, making it the oldest angiosperm ever documented, and two other trees - Dorslandboom in Namibia and Glencoe in South Africa - were estimated to be approximately 2,000 years old.^[24] Another specimen known as Grootboom was dated and found to be at least 1275 years old.^[20][25] The Glencoe baobab, a specimen of A. digitata in Limpopo Province, South Africa, was considered to be the largest living individual, with a maximum circumference of 47 m (154 ft)^[26] and a diameter of about 15.9 m (52 ft). The tree has since split into two parts, so the widest individual trunk may now be that of the Sunland baobab, or Platland tree, also in South Africa. The diameter of this tree at ground level is 9.3 m (31 ft) and its circumference at breast height is 34 m (112 ft).^[24]

Two large baobabs growing in Tsimanampetsotse National Park were also studied using radiocarbon dating.^[24] One called Grandmother is made up of three fused trunks of different ages, with the oldest part of the tree an estimated 1,600 years old. The second, "polygamous baobab", has six fused stems, and is an estimated 1,000 years old.^[24]

Food uses

The cut fruit from Mozambique

Baobab powder

Baobob flower

Leaves

Leaves may be eaten as a leaf vegetable.^[20]

Fruit

• The white pith in the fruit of the Australian baobab (A. gregorii) tastes like sherbet.^[27] It has an acidic, tart, citrus flavor.^[28] It is a good source of vitamin C, potassium, carbohydrates, and phosphorus.^[29]
• The dried fruit powder of Adansonia digitata, baobab powder, contains about 11% water, 80% carbohydrates (50% fiber),^[30] and modest levels of various nutrients, including riboflavin, calcium, magnesium, potassium, iron, and phytosterols, with low levels of protein and fats.^[28][31][32]Vitamin C content, described as variable in different samples, was in a range of 74 to 163 milligrams (1.14 to 2.52 gr) per 100 grams (3.5 oz) of dried powder.^[28] In 2008, baobab dried fruit pulp was authorized in the EU as a safe food ingredient,^[33] and later in the year was granted GRAS (generally recognized as safe) status in the United States.^[34]

• In Angola, the dry fruit of Adansonia digitata is usually boiled and the broth is used for juices or as the base for a type of ice cream known as gelado de múcua.
• In Zimbabwe, the fruit Adansonia digitata is used in traditional food preparations which include "eating the fruit fresh or crushed crumbly pulp to stir into porridge and drinks".^[35]

Seed

• The seeds of some species are a source of vegetable oil,^[36][37]
• The fruit pulp and seeds of A. grandidieri^[36] and A. za are eaten fresh.^[37]

Tree

In Tanzania, the dry pulp of A. digitata is added to sugarcane to aid fermentation in brewing (beermaking).^[38]

Other uses

Some baobab species are sources of fiber, dye, and fuel. Indigenous Australians used the native species A. gregorii for several products, making string from the root fibers and decorative crafts from the fruits.^[39] Oil from the seed is also used in cosmetics, particularly in moisturizers.^[40]

Gallery

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  Adansonia digitata

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  Adansonia gregorii

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  Adansonia rubrostipa

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  Adansonia suarezensis

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  Adansonia digitata leaf

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  Adansonia digitata flower

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  Adansonia digitata hanging fruit

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  Adansonia rubrostipa, inside the fruit

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  Adansonia digitata seeds from the fruit

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  Elements of the fruit pulp of Adansonia digitata (clockwise from top right): whole fruit pulp chunks, fibers, seeds, powder from the pulp

References

External links

• Media related to Adansonia at Wikimedia Commons
• Data related to Adansonia at Wikispecies