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Erythrina, ‘The Coral Trees’ and their utility in Analog Forestry design.

by Ranil Senanayake

The genus Erythrina ( fam: Leguminosae) is represented by over 100 species , distributed throughout North and South America, Australia, Africa and Asia and are among some of the easiest plants to grow. They are commonly known as coral trees on account of their brilliant blossoms ranging from an intense red to mixtures of red and yellow. Although the primary use of this genus has been for ornamental purposes, a few species have excelled as utility species.

Pic Above : E.edulis : hugely nutritious food pods are a yield of this tree along with other benefits to the landscape.

In Sri Lanka the genus is represented by one species in the native flora Erythrina indica. This species is found from sea level to about 200m asl and is sparsely scattered through the Island both as a household and a feral tree. It is a medium sized quick growing tree with thorny stems and branches. Like most members of the genus it possesses trifoliate leaves. It is a deciduous species in leaf habit and looses all its leaves in the dry season. Masses of scarlet flowers appear at the tips of the branches following leaf fall making the tree a very striking sight.

Many exotic species of Erythrina verigata (pic above ) have been introduced over the last century into the National Botanical Gardens or to private agricultural ventures, but only two species are utilized to any extensive degree, E.indica and E.lithosperma (pic below) .

In anthropogenic use, these trees are commonly met with as an occasional household tree and utilized for the provision of fodder, fence posts and fuelwood. The genus is widely utilized in the plantation sector where it is used as a medium shade tree for the provision of shade or as a nurse tree for the provision of nitrogen to the soil. The agronomic benefits of this plant association have been well demonstrated.

They include,

(1) Supplying the soil with bulky organic matter to replace the rapid and heavy losses of organic matter from soils in the tropics.

(2) Making available nitrogen and

mineral nutrients in a constant but slowly available form

(3) Maintaining the soil structure and microbial populations. While this genus provided a multiplicity of ecological uses, it is not generally used in human food systems due to the fact that all species of the genus, except one possess seeds that are toxic to humans.

The exception is Ertyhrina edulis of the Andean foothills in South America.

Erythrina edulis is A moderate sized tree 8-10 m tall with conical spines on the trunk, young branches are thorny. Leaves are trifoliate and posses small soft spines. The two petalled fleshy flowers face upward forming a conical cup in which nectar gathers. Two varieties are commonly met with, the differences being in the color of the flowers one is red the other is light orange.

This species is found between 1000 - 2700 meters asl within its range from western Venezuela to southern Bolivia. It is a vigorous, fast growing , pioneer species that colonizes newly cleared sites.

The pod is almost cylindrical, about 20-30 cm long, greenish purple in color, smooth on the outside. The skin is spongy and encloses 1-10 large, light brown, glossy seeds 2.5-3.5 cm in diameter. The seeds contain about 20 percent protein on a dry Wt basis. The seeds are highly nutritious (table 3) and contain more essential amino acids than beans or peas (table 4 ). They have a good balance of inorganic nutrients particularly phosphorus.The pods are produced twice a year. As they mature at slightly different times many pickings are necessary. A single tree has been estimated to yield about 200Kg of seed each year (20 kg of bean harvested has been recorded from a single specimen at Belipola demonstration ). In an economic and social sense, the addition of E.edulis to the tea agroecosystem can generate the production of food grade beans in the excess of 3000 Kgs per hectare per annum.

As the seeds contain about 20-30% protein E. edulis is a very promising candidate to provide a new source of protein to both Urban and rural communities.

The protein content (N x 6.25) of the seeds of Erythrina edulis (balú) varies between 18-21%; when the fraction corresponding to non-protein nitrogen is extracted with trichloroacetic acid (10%), this value decreases to 14-15%. Remarkable differences in the distribution of the protein fractions are observed when two schemes of extraction are assayed. The amino acid analysis shows that this legume has similar or higher amounts of most amino acids than those present in other leguminosae; the calculated chemical score and protein score show that methionine is the first limiting amino acid and tryptophan, the second. The protein efficiency ratio (PER) of thermically-treated flours has the highest value at 30 minutes of treatment (1.15)

Pic Above : Planting E. edulis as the low shade tree at the Haldunmulla Estate tea production area (Field # 2 ) in 2022,

The Erythrina edulis tree is available at the Belipola Arboretum tree-nursery and can be observed to support mature native epithetic orchids at the Belipola Analog Forest demonstration (Pic below)

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