About

Aeschynomene elaphroxylon, also known as an ambatch, pith-tree, balsa wood tree, or umburu, is a common large shrub to small tree in the genus Aeschynomene in the family Fabaceae, growing in swamps, lakes and rivers in Tropical Africa. This is an unusual leguminous tree in that it grows in water as a freshwater mangrove, with an extremely lightweight wood acting as a float and a specialised root system sprouting from the trunk which forms a tangled web hanging through the water and sprawling through the mud. It has adventitious roots and roots which are differentiated into special structures adapted to the swamp environment. It can even grow as floating islands of drifting forests.

The name 'ambatch' derives from the name of the plant in the Arabic dialect spoken in Nigeria known as Shuwa by the British.

How to grow it

Of all the aquatic Aeschynomene species, especially Ae. elaphroxylon is larger-flowered, and has therefore been planted as an ornamental plant in some areas.

It has been cultivated in Malaysia, Sri Lanka, and South America. It has also been grown as an ornamental plant in Bogor on Java, at least in the 1950s or earlier. It is said to be cultivated in Egypt, as it was said to be studied in the Nile in 1891 by Klehbahn during the British military occupation of the country. In actually, Klehbahn was sent specimens of the plant by the explorer Georg August Schweinfurth, who was in Cairo at the time and related that a number of fine specimens were grown there in a small basin in the botanical garden of the medical school, in such a luxuriant state as he had not seen during his travels in the upper Nile and beyond. The plant was also grown in the botanical garden in Berlin in the 1880s, but this accession died despite the best efforts of Ignatz Urban; cuttings from Schweinfurth were later grown here.

Where it grows

Aeschynomene elaphroxylon is indigenous to most of tropical Africa, and is also found in Madagascar, where it was possibly naturalized. In Madagascar it is found in Mahajanga and Toamasina Provinces, and grows in dense stands along the shoreline of Lake Alaotra. It occurs southwards to northern Mozambique, southern Malawi, northern Zimbabwe to Angola.

Uses

Although it is sometimes seen as a weed, the conical poles are also harvested for various purposes. The spongy wood, often mistakenly termed pith, is lighter than cork, yet very resistant to rot. Unlike pith, it contains thick tree rings. It is extremely lightweight and soft. The trunk wood is traditionally used to make floats for fishing nets, and used in raft, canoe and boat construction, for example around Lake Chad. The trunks were cut in 30 cm long sections for use as net floats in coastal Senegal already in the 1820s. At least in the 1950s, sandals were manufactured from the wood in Ghana, as well as screens for blocking the sun. Some French entomologists also used thin slices of the wood as a base in which to pin their specimens in the early 1800s.

Other Aeschynomene plants

Shyleaf · Sola pith plant · Shrubby jointvetch · Indian jointvetch · Zigzag jointvetch · Virginia jointvetch · Jointvetch