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2.6 Erythrina Species - Pantropical Multipurpose Tree Legumes

D.L. Kass


Introduction
Botanical Description
Origins
Environmental Adaptation
Establishment and Cultivation
Production and Management
Utilisation of Erythrina
Conclusions
References


Introduction

Unlike many other genera of forage tree legumes, Erythrina is pantropical, consisting of some 112 species, 70 neotropical, 31 African and 12 Asian. Only one species, Erythrina fusca, occurs in both the New and Old Worlds. The genus is probably of South American origin but the ability of the seeds to float and retain viability after prolonged immersion in salt water and the probable riverine, coastal or estuarine environments inhabited by the ancestral species have resulted in worldwide distribution. Pollination by birds and a marked ability to hybridise have resulted in a tremendous amount of ecological and morphological diversity, both within and between species, but within rather close cytological and phytochemical relationships. The alkaloids of Erythrina are distinct from those of other legumes and they all possess an unusual high activity, low affinity nitrate reductase system distinct from known nitrate reduction patterns in other angiosperms (Neill 1988). The base chromosome number of n = 21, shared by all Erythrina species that have been counted, is found in no other legumes.

Botanical Description

Erythrina L. species are distributed throughout the tropics and extend into warm temperate areas such as South Africa, the Himalayas, southern China, the Rio de la Plata region of Argentina and southern United States. Most species are trees or shrubs but about ten species which occur in climates with pronounced dry and/or cool seasons are perennial herbs with large, woody rootstocks. Because of their characteristic trifoliate leaves, Erythrina has been placed traditionally in the subtribe Erythrininae of the tribe Phaseoleae (Neill 1988). The trunk, young branches, petioles and petiolules are often armed with blunt, conical thorns or recurved prickles. Leaves are pinnately trifoliate, often clustered at the ends of branches; leaflets are broad-ovate, elliptic, often deltoid or rhomboid, entire, lateral leaflets often asymmetric, terminal leaflet largest, symmetric; stipels are fleshy, glandlike, turning black upon drying, usually one at base of lateral leaflets, paired stipels at base of terminal leaflet; stipels are small, ovate, or linear, caducous or persistent. Erythrina species exhibit great diversity in floral structure, inflorescence orientation, fruit morphology, seed coat coloration, and vestiture and epidermal ornamentation of foliage and calyces. Flowers appear before or with the first leaves, very showy, mostly red, some salmon, pink, orange or yellow, solitary, paired or fasicled in erect, terminal racemes leafy at the base or in axillary racemes (Allen and Allen 1981) (Figure 2.6.1).

The diversity of floral structure reflects adaptation to different pollination mechanisms. All Erythrina species have red or orange flowers with copious nectar and are adapted to pollination by nectivorous birds. All 42 paleotropical and some 15 of the neotropical species are pollinated by 'perching birds' of the order Passeriformes; inflorescences of passerine-pollinated species are oriented in such a way that the birds can perch while feeding on the floral nectar. The corolla standard is usually broad and the flowers are open with exposed reproductive parts. Pollen is deposited on the feeding bird's breast. The diversity of size, form and orientation of passerine-pollinated Erythrina flowers would appear to reflect variation in the size, morphology and behaviour of the pollinators (Neil 1988). The remaining 55 neotropical species are pollinated by hummingbirds (Trochilidae). The corolla standard of hummingbird-pollinated Erythrina is narrow and conduplicately folded to form a 'pseudotube' concealing the wing and keel petals as well as the reproductive parts. The flower resembles the tubular corollas of many gametopetalous hummingbird-pollinated plants but the pseudotube is not sealed on the ventral side where the margins of the corolla standard meet. The inflorescence of the hummingbird-pollinated species is erect, and the flowers are oriented outward, providing no perch for the hummingbirds, which are the only nectivorous birds which hover while feeding.

Origins

The origin of Erythrina, like its relationship to the rest of the Leguminosae, is obscure. No fossil record of the genus has been reported. Distribution patterns, pollination and dispersal mechanisms and the known history of the Leguminosae indicate an upper Eocene to upper Oligocene origin for the genus (30-40 million years ago) followed by ocean-drift or other long-distance dispersal among the tropical regions of America, Africa and Asia-Oceania. Much diversification of Erythrina has occurred independently in Africa and America and to a lesser extent in Asia. South America seems the most likely place of origin since the majority of putative ancestral groups within the genus occur there. Africa is a possible candidate because it also contains a number of endemic groups. Although Erythrina almost certainly originated after the breakup of Gondwanaland, it has a basically South American-African distribution that is shared by many angiosperms including the Leguminosae as a whole. The Erythrina taxa in 'tropical Laurasia', i.e. Asia and Mesoamerica, are clearly derived groups. In Mesoamerica, the genus has undergone extensive recent speciation within a single lineage (Neill 1988).

Fig. 2.6.1. Leaves, flower and pod of Erythrina fusca.

The origins of Erythrina beyond the species level are somewhat difficult determine. Erythrina fusca is the only species to occur in both the neotropics and paleotropics. With its wide distribution and presumably primitive features, E. fusca or a fusca-like ancestor may represent the original progenitor of the entire genus. The other species of the subgenus Microptaryxx are confined to South America in the Orinoco, Rio de la Plata and Amazon basins, thus indicating riverine areas of South America (Neill 1988) as a possible source of origin.

Environmental Adaptation

Erythrina can presumably be found anywhere in the tropics or subtropics with the possible exception of extremely dry areas although Erythrina species are apparently found in the Kalahari desert of southwest Africa. Several species are limited to specific ecological zones. Erythrina edulis occurs only in high elevations of the Andes, where it is used as human food. Erythrina fusca is found throughout coastal regions of the tropics where it shows considerable tolerance to flooding and saline conditions. Erythrina berteroana is widely used as a live fence from sea level to elevations of 2,000 m in Central and South America with rainfalls ranging from 800 to 5,000 mm per year. It has also shown tolerance to soils with high aluminium saturation. Production of 12-16 t/ha/year has been maintained by selected clones of E. peoppigiana and E. berteroana on a soil with pH 4.0 and 50% aluminium saturation (Typic Fulvudand) near Turrialba, Costa Rica (Camacho et al. 1993). An Erythrina species, presumably E. berteroana, also showed considerable tolerance to a soil with even higher levels (75%) of aluminium saturation in Yurimaguas, Peru (Salazar and Palm 1987). Another widely distributed species, E. variegata, the most utilised Erythrina on the Indian subcontinent, is a coastal-strand, ocean-dispersed species similar to E. fusca found all along the Indian Ocean from Madagascar to Indonesia and extending to New Guinea, Polynesia, Micronesia and the Marquesas (Neill 1988).

While generally considered intolerant of frosts, two species, E. herbacea and E. flabelliformis, extend into the southern United States where they exist as herbaceous perennials whose above-ground stems die back each winter. An Asian species, E. aborescens, occurs in Himalayan forests and in the mountains of western China to 3,000 m elevations and is evidently highly tolerant of frosts. Three sections of the subgenus Erythrina endemic to southern Africa, encompassing five species, E. caffra, E. lysistemon, E. humeana, E. zeyheri and E. acanthrocarpa, show some degree of frost tolerance. It is also presumed that the South American species, E. berteroana and E. edulis, which are common at high elevations where frosts generally occur, are also frost tolerant.

Establishment and Cultivation

Erythrina is traditionally reproduced from large cuttings although seeds are usually viable. Due to the high level of outcrossing, there should be considerable variability in trees produced from seed. It has been shown in Mexico, that a hummingbird must visit more than one tree per day to obtain sufficient energy (Neill 1987), resulting in a high degree of hybridisation While large cuttings are generally used for establishment of live fences and shade for plantations (Ramirez et al. 1990, Hegde 1993), seed is generally used when E. variegata is utilised as a support for vine crops such as betel (Piper biter), black pepper (Piper nigrum), vanilla (Vanilla fragrans), grapes (Vitis spp.) and yams (Dioscorea spp.). In India, this is the most important use of the species (Hegde 1993). The trees are usually established by planting two or three seeds directly in each pit or by planting seedlings raised in a nursery. Since spiny forms are favoured for support purposes and non-spiny forms for shade, use of vegetative propagation may be a means of ensuring non-spiny forms. However, rapid establishment is generally a priority when used for shade or live fences, favouring the use of large stakes. Smaller stakes may be used for other purposes such as protein banks where it has been found that planting 60 cm long stakes laid horizontally has resulted in good establishment.

Production and Management

Erythrina spp. are universally recognised for their high biomass productivity and utilisation almost always involves frequent pruning. When used as a support tree for pepper vines, E. variegata may be pruned at 6-8 week intervals; when used as a coffee shade or in live fences, it may be pruned once yearly, while for timber or pulpwood, the tree may be left to grow for 25 years without pruning (Hegde 1993). In Costa Rica, E. peoppigiana in coffee plantations is generally pruned twice yearly while E. berteroana and E. fusca in living fences are generally pruned once yearly. Experimental work has shown that E. berteroana can be pruned at intervals of 4 months to produce higher quality forage for ruminants. Pruning at more frequent intervals will reduce biomass yield over time (Pezo et al. 1990). As early as 1934, Joachim and Kandiah (1934) determined that cutting E. lithospermum at intervals of 5 months would maximise nutritional content of green manure materials in Sri Lankan tea plantations.

Utilisation of Erythrina

Although species vary with region, the general uses of Erythrina are principally as a shade and support tree, followed by live fences whence it can be used for green manure and animal feeding. Some species are used as ornamentals; flowers are frequently eaten or used to make tea, and seeds for jewellery. The wood is too light and porous for most purposes but it finds special uses for surfboats, canoes and carving.

Shade and support tree

Throughout the world, the principal use of the genus Erythrina is as a shade and support tree. Erythrina fusca is widely appreciated as a cocoa shade throughout the Americas, principally because of its adaptation to humid areas where cocoa is generally grown. Erythrina burana is a component of the forest in the original range of Coffea so the use of Erythrina as a coffee shade may date to the domestication of the crop (Teketay 1990). Erythrina variegata is used in India as both a coffee and cocoa shade while E. poeppigiana was introduced to Costa Rica early in the 20th century as a coffee shade. It successfully replaced Inga species traditionally used in the more humid zones of Costa Rica. Nutrient cycling studies with coffee and cocoa under shade of E. fusca or E. poeppigiana have demonstrated the value of these species in Brasil, Costa Rica (Fassbender 1987, Alpizar 1987, Fassbender et al. 1991) and Venezuela (Herrera et al. 1987). Erythrina species are favoured for shade because of their rapid establishment and high biomass production. With increasing labour costs and falling cocoa and coffee prices, some of these advantages have become less favourable in recent years and Erythrina has either been replaced by or combined with shade species requiring less frequent pruning or which produces marketable by-product such as fruit or timber.

Live fences

Various Erythrina species are used in live fences. Erythrina berteroana, E. fusca, E. peoppigiana, E. costarricensis are widely used in Central America (Budowski 1987). Erythrina golmani, E. chiaspasana, E. folkserii and E. pudica are widely used in southern Mexico (Neill 1988). One species commonly found in fence-rows, E. caribea, is apparently sterile and is propagated by taking cuttings from existing fenceposts. Erythrina variegata is favoured as a live fence in southern India because, as the trees have little value as fuel, they are rarely stolen (Hegde 1993) (Figure 2.6.2). Although live fences can be pruned at intervals of 4-5 months, the relatively low population of trees in a live fence restricts the value of this practice as a source of animal feed. Cut at 4 month intervals, a live fence of E. berteroana produced 1.7-4.0 t/ha/km of dry matter compared with 1.0-5.6 t/ha/km for Gliricidia sepium (Pezo et al. 1990).

Fig. 2.6.2. Erythrina variegata used as a living fencepost in Western Samoa.

Large stakes (2-2.5 m) are almost universally favoured for live fence production so that cattle will not eat the young sprouts (Viquez et al. 1993). The lower part of the stake (20-40 cm) is buried in the soil at planting. The top is cut at a diagonal to avoid water accumulation. If the soil is soft, the bottom of the stake can be cut to a point and the stake driven into the ground. If the soil is hard, a hole should be dug. If drainage is poor, small incisions should be made in the bark below the soil level to increase rooting (Viquez et al. 1993). Farmers generally favour cutting posts with the waning moon and planting with the waxing moon although no scientific basis for this practice has yet been determined.

Livestock forage

There has been considerable research on Erythrina species as livestock forage even though most species, with the apparent exception of E. edulis, have yielded alkaloids having curare-like poisoning action (Allen and Allen 1981, Payne 1991). However, these alkaloids appear to be more concentrated in the seeds and bark than in the leaves. In a study of alkaloid content of different clones of the species E. berteroana, E. poeppigiana and E. costarricensis, Payne (1991) identified the major alkaloid as b -erythroidine, a naturally derived drug used in the 1950s and 1960s as a neuromuscular blocking agent in surgery and electroshock treatments. Other biologically active alkaloids identified were a-erythroidine, erybidine, erythraline, erysodine and oxo-b -erythroidine. There was a difference of more than two orders of magnitude in the b -erythroidine contents of the clones of the species tested, indicating at least partial genetic control of the alkaloid content. A feeding study performed with goats demonstrated that the b -erythroidine present in the foliage of Erythrina species is hydrogenated in the rumen and that these metabolites are detected in milk. Synthetic studies showed that the dihydroerythroidine isomers present in the milk and rumen samples were not the same isomers produced by catalytic hydrogenation. The toxicology of the rumen and milk derived compounds is therefore unknown (Payne 1991).

Of the Erythrina species utilised in Costa Rica, E. peoppigiana has the highest crude protein content (42%), protein solubility (49%) and in vitro dry matter digestibility of edible biomass followed by E. berteroana and E. costarricense. The lowest values are found in E. fusca. There is considerable variability in the nutritive value among clones of these species, especially E. berteroana (Pezo et al. 1990). In E. berteroana, E. costarricense and E. fusca, a greater percentage of the nitrogen is linked to the acid-detergent fibre, resulting in lower protein availability and less degradation of the protein in the rumen. All Erythrina species tested had relatively high cell wall contents (61%) when compared with other forage legumes although the levels of lignification (17%) were similar. Diets which contain Erythrina should therefore contain supplemental energy sources which are readily degradable in the rumen (Kass et al. 1993).

Ruminants find the foliage of the various Erythrina species used in Costa Rica more palatable than G. sepium. Higher milk yields were obtained in goats fed E. peoppigiana (1.26 kg/animal) than G. sepium (1.11 kg/animal) due to differences in intake. Supplemental E. peoppigiana foliage did not result in as great a weight gain in calves or milk production of cows as those fed soybean or fish meal. However, economic analyses indicated that greater returns to the farmer were obtained from using legume tree foliage and locally available energy sources such as green bananas (Pezo et al. 1990).

Source of green manure

Farmers recognise the value of Erythrina mulch for improving soil fertility. Farmers have responded quite favourably to the planting of E. fusca along contour lines in crop fields in Costa Rica (Hernandez 1993). Erythrina species have figured in almost all alley farming studies carried out in Latin America (Alavez 1987, Kass 1987, Salazar and Palm 1987, Kass et al. 1989, Sanchez 1989, Jimenez 1990, Nygren 1990, Delgadillo et al. 1991, Garzon 1991, Haggar et al. 1991, Jimenez et al. 1991, Salazar 1991, Szott et al. 1991, Lebeuf 1993, Soto et al. 1993).

Despite its reputation for high biomass production, Erythrina has generally produced less biomass in alley farming experiments than other nitrogen fixing trees (G. sepium and Inga edulis). Nutrient return from Erythrina to alley cropping systems varied with soil type and was substantially higher on more fertile soils (Table 2.6.1). Kass et al. (1989) estimated nitrogen fixation at 50 kg/ha/year during a 30 month period.

Human food

Despite the alkaloid content, the flowers of many Erythrina species are consumed in Mesoamerica. Erythrina edulis in the Andean regions of Colombia and Peru would appear to be the only species whose seeds are eaten. The seeds are ground into flour to make a variety of products (Federacion Nacional de Cafeteleros 1991).

Table 2.6.1. Annual contribution of nutrients from Erythrina in alley cropping systems on three soil types (kg/ha/year).

Soil type


Nutrient

Reference*


N

P

K

Ca

Mg

Typic Humitropept

278

24

156

82

34

1

Paleudult

69

8

38

16

8

2

Tropofluvent

489

61

362

274

64

3

* References: 1. Kass et al. (1989); 2. Szott (1987); 3. Salazar (1991)

Medicinal uses

Erythrina has been used in folk medicine for treatment of insomnia malaria fever, venereal disease, asthma and toothache. South American Indians used Erythrina as a fish poison. In addition, there are reports of its use as a narcotic and antihelminthic. The first compounds isolated from Erythrina were alkaloids. b -Erythroidine was used for a brief time as a muscle relaxant in surgery and in treatment of schizophrenia Tea from Erythrina flowers is regularly used as a relaxant in Mesoamerica. Subsequently, homoerythrina alkaloids were investigated for their anti-cancer activity. Recently, research involving Erythrina has focused on other chemical effects, primarily the antimicrobial action of Erythrina lectins and the enzymology of proteinase inhibitors isolated from Erythrina (Payne 1991).

Ornamental

Various species of Erythrina, known as coral trees, are used as ornamentals in California, Mexico, South Africa, India, Australia and Pacific countries.

Wood

Erythrina wood is greyish white, spongy, lightweight and strong but not durable. It is used for sieve frames, surfboards, dugout canoes, outrigger canoe floats, boxes and small art carvings. Erythrina monosperm Gaud. is a favourite canoe wood of the Polynesians. The dry wood of this species and the bark of E. suberosa Roxb. are used for the manufacture of composition cork (Allen and Allen 1981).

Conclusions

Despite the alkaloid content, Erythrina foliage continues to be fed to cattle and goats around the world without reports of ill effects. Use as a non-ruminant feed is probably risky. It has high biomass productivity and is frequently used as a living fence, shade or support tree. However, Erythrina requires constant pruning in support and alley farming systems (Muschler 1991). Increasing labour costs have made this a less attractive feature of the genus and its use in shaded plantations is decreasing. Insect pests are sometimes a problem (Salazar and Palm 1987). It serves as an alternative host for Phyllophaga in Central America and the fruit piercing moth Othreis fullonia in the Pacific islands. The latter pest has slowed its introduction in the Pacific.

References

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