Avicennia germinans
Unique Black Mangrove in the Everglades National Park
The Black Mangrove ( Avicennia germinans ) is a mangrove, which occurs in the tropics and subtropics of America and West Africa. It belongs with the Red Mangrove ( Rhizophora mangle ) and white mangrove ( Laguncularia racemosa ) the dominant tree species of the mangrove vegetation in these areas. Striking for the entire genus Avicennia are pencil-thin breathing roots that protrude at regular intervals from the ground and used for oxygen supply to the root system. Stilt roots as with other mangrove species are not formed. The leaves have glands that secrete a salt-containing liquid so as to regulate the salt concentration in the tissue. Of all the species Avicennia the black mangrove is the largest flowers.
- 3.1 salt balance
- 3.2 Respiratory roots
- 3.3 pollination and dispersal
- 3.4 Community
- 7.1 Literature
- 7.2 Notes and references
Description
Appearance
The Black Mangrove is 40 centimeters reached an evergreen tree, the plant height of 25 meters and trunk diameter ( DBH ). Often its dimensions are smaller, so he reached in Puerto Rico plant height 3-13 meters and trunk diameter of 30 centimeters. Near the northern border area in Florida, the species grows shrub-like. The trunk is otherwise mostly crooked and short, wide spreading crown.
Bark and wood
The bark can be black, dark brown to reddish brown or gray, showing his occasional Korkporen ( lenticels ). It is something along cracked and dissolves into thin flakes off. Characteristic of the type is the yellow -to-orange inner bark.
The wood is very hard and somewhat oily. It has a bright, fairly wide sapwood, the heartwood is dark brown. Like the other species of the genus Avicennia has the Black Mangrove abnormal secondary growth: The wood shows regular growth zones that are no annual rings, however. Each ring consists of xylem, phloem and a transition tissue, which stands out as a white stripe. The width of the growth rings is not affected by climate or other environmental factors, the annual number of newly formed rings varies.
Root system
In the usually soft substrates flat running roots are formed that extend far beyond the crown diameter. Note the typical Avicennia species breathing roots ( pneumatophores ), which are formed as upright (ie, negatively - geotropic, against gravity growing ) lateral roots in large numbers and at regular intervals 15 to 30 centimeters on the long main roots. They rise up to 30 centimeters from the ground, are as thick as a pencil and supply the root zone with oxygen from the atmosphere. From a tree with a height of two to three meters about 10,000 pneumatophores are formed. The root system is in addition to the horizontally extending main roots and pneumatophores or from the positive geotropic - growing lateral roots, which are used for absorption of nutrients and for anchoring. Stilt roots as the Red Mangrove ( Rhizophora mangle ) are not formed.
Branches and leaves
The branches are divided into 1-9 cm long internodes with approximately square cross-section, which are separated by considerably thickened nodes. Of the higher-lying branches of strong trees numerous aerial roots are formed.
The decussate arranged on the branches leaves are leathery, narrowly elliptic and entire. They are 4,5 to 15 centimeters long and 1.8 to 4.5 inches wide. The short petioles are 2-27 mm long and the top side rinnig stiffened, the underside is convex. The Leaves are deep green to yellow- green and glossy, the lower gray-green and densely covered with silvery fine hairs. The Apex can be both pointed and blunt, the Spreitenbasis is tapered wedge-shaped. Characteristic are often visible on the leaf blades of salt crystals. The excess salt is discharged by microscopic salt glands in the leaves.
Flowers
The Black Mangrove forms the largest flowers in the genus Avicennia. It flowers in loose, rare dense, terminal or axillary, aged men, 1.5 to 6.6 centimeters long and 1 to 1.5 inches wide inflorescences, each with one to 15 flowers. The small, hermaphrodite, zygomorphic, sweet-scented flowers are 1 to 2 inches long. The five bright green, 3-5 mm long sepals are fused pitcher shaped. The four white, cream-colored or yellowish petals are fused bell-shaped, the corolla has a length of 12 to 20 millimeters. There shall be four in favor of grassroots of the petals stamens. The stamp has a two-lobed stigma. The Black Mangrove provides abundant nectar and thus attracts a large number of insects. The main flowering period in the Caribbean and Florida during the months of May to July.
Fruits
There are round to elliptical, thin-walled, light green, 2.5 to 3.8 cm long and 7-13 mm wide fruit capsules formed. They contain a single seed without testa and without endosperm. It consists only of the embryo with two large, greenish, folded cotyledons, a thick radicle ( radicle ) and one with the naked eye can not be seen scion bud ( plumule ). You seed maturity falls mainly in the months of September and October.
Distribution and habitat requirements
One finds the Black Mangrove in America and West Africa. Its area of distribution in America includes the West Indies, including the Bahamas without Dominica, both coasts of Central America, the Pacific coast of South America to Ecuador and the offshore island groups of the Galápagos Islands, and the South American Atlantic coast to Brazil. In the U.S., their natural occurrence extends to southern Florida, the Mississippi Delta and Texas. In West Africa, one finds the way to the Atlantic coast of Mauritania to the Democratic Republic of Congo.
The natural occurrence is limited to seacoasts. Locations at an altitude of 15 meters as on the coast of El Salvador are an exception. The species grows in brackish water area protected, muddy coasts, particularly in the mouth region of rivers. It tolerates high salt concentrations, but also grows on freshwater and requires no salt. It prefers soils with pH values from 5.3 to 7.8. The Black Mangrove is like other mangroves a kind of the tropics. Occurrence in the subtropics are exceptions. These can be found in warm ocean currents emanating from densely populated tropical areas and run along island chains, and so favor the spread. These conditions are given in the subtropical part of Florida.
The Black Mangrove is listed in the IUCN Red List as not at risk ( "Least Concern" ).
Ecology
Mangrove forests occur on tropical and subtropical coastlines. Your environment is characterized by the salt water, the tides, through the underground consisting of oxygen-poor mud and by high temperatures and high humidity.
Salt balance
Mangrove roots in salzwasserhältigem ground, so they are halophytes. Because high salt content of the plant damage, the accumulation in the tissue is prevented. Even with the inclusion of water through the roots only a small part of the salt is added, however, representatives of the genus Avicennia absorb a lot comparatively ( compared eg with Rhizophora mangle ). The salt content in the xylem reached values of approximately 10% of the salt content of seawater. To avoid to high concentration of salts, the excess salt is precipitated by salt glands at the blade top and bottom sides. During the rainy season the salt content of the excreted fluid may reach half the salinity of sea water, in the dry season, the salinity correspond to that of seawater. Per square meter of leaf area and day, about 0.2 to 1.2 grams of salt are discharged. It is washed away by rain or, if the water of the separated liquid to evaporate, crystallize on the leaves.
Breathing roots
The bottom of the mangrove forests mostly consists of oxygen-poor mud. To ensure the supply of oxygen to the root system, are representatives of the genus Avicennia breathing roots called pneumatophores formed. This project at least at low tide from the water and have contact with the atmosphere. Gas exchange takes place by Korkporen breath roots, the further transport through cavities, which can account for 40 % of the total volume of the root system.
Pollination and dispersal
The main flowering season falls in Florida and the Caribbean in the months of May to July. Pollination is by insects, mostly bees. Germination begins as in the genus Avicennia usual, attached to the tree in the fruit, without the seedling fruit leaves ( Kryptoviviparie ). The seeds ripen from September to October, this fruit can be transported far from the flow. Seedlings can survive drifting a very long time.
Community
Mangrove forests are usually divided into zones, which are characterized depending on the proximity to the sea through different ways. After the Red Mangrove Mangrove blacks settled together with the White Mangrove ( Laguncularia racemosa ) the next further inland zone, which is only achieved by high accrual of floods. The distribution area of the species Avicennia schaueriana, on the Pacific coast of Central America with Avicennia bicolor and Avicennia tonduzii overlaps on the South African east coast. Many fish and crustaceans are the mangroves as a breeding ground, where the root system provides protection and foliage food, such as the square crab Goniopsis cruentata or the mangrove crab Aratus Ucides cordatus and pisonii. Ibises, pelicans and several species of herons have their nesting grounds in the mangrove forest.
System
Genetic studies indicate a closer relationship between copies of the east coast of America and the west coast of Africa as between the two opposite coasts of America. This points to the maintenance of genetic exchange across the Atlantic. However, the differences among the specimens of the west coast of America are not so large that a subdivision into subspecies would be justified. From the way even the form Avicennia germinans guayaciliensis can be distinguished var. It occurs on both the western and eastern coast of America, which speaks for the separation even before the formation of the land bridge between North and South America.
The genus Avicennia was counted earlier to the family of verbena family ( Verbenaceae ). Today it is regarded as a separate family Avicenniaceae or provided as a subfamily Avicennioideae into the family of Acanthaceae ( Acanthaceae ).
Botanical history
The Black Mangrove became known parts of plants, which were collected by the Irish physician and botanist Patrick Browne in Jamaica, in Europe. Parts of it with another of Venezuela were used in 1759 by Carolus Linnaeus to describe the species as Bontia germinans in the tenth edition of Systema naturae, his work ( basionym ). He used in the 1763 published the second edition of his Species Plantarum the name also of plant parts from India, which he had described in the first edition as Avicennia officinalis. As soon became apparent that there are two types, the name of Avicennia nitida by Nikolaus Joseph von Jacquin has been established for the American way. In West Africa the kind of Palisot de Beauvois has been described as a separate species Avicennia africana. In 1960, differences between the African and American representatives were led in color and form of dried leaves of Herbarexemplaren. Today, the West African representative of the species Avicennia germinans also be attributed to what is confirmed by molecular studies. The name of Avicennia africana and Avicennia nitida are synonyms.
The genus name Avicennia reminiscent of the Persian philosopher Avicenna, the epithet germinans means " sprouting " and refers to the germination of the seed still on the tree.
Use
The wood can be due to its hardness is difficult to edit and wood dust causes skin inflammation. Therefore, it is rarely used, as previously for the manufacture of furniture. Today it is rarely used as a timber, as telegraph poles or bridges, jetties and railway sleepers. One uses it as fuel and it can be processed into charcoal. The wood has a high bulk density of about 950 kg / m³, it is durable but not resistant to termites.
The Black Mangrove is a profitable bee pasture and causes a pure, white honey, which is known as the " Mangrove Honey" in Florida. The excreted through the leaves salt crystals can be used for seasoning food. Two leaves enough for a bowl of broth. The seeds are poisonous raw, but can be eaten cooked, but this is done only in times of famine.