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Pongamia is a genus of legume in the Fabaceae family. Recently it has been proposed that the genus Pongamia be rejected in favor of the genus Millettia, and many species have been reclassified. Due to recent interest in biofuels, pongamia is often the generic name given for Millettia pinnata, a tree being explored for producing biodiesel.
Botany and description
- Derris indica (Lam.) Bennett
- Millettia novo-guineensis Kane. and Hat.
- Pongamia glabra Vent. Pongamia pinnata Merr.
Species formerly in the genus
- Pongamia ovalifolia is a synonym for Millettia peguensis
- Pongamia pinnata or Pongamia glabra are synonyms for Millettia pinnata
- Pongamia uliginosa is a synonym for Derris trifoliata
In 1834, Robert Wight and George Arnott Walker-Arnott, both Scottish botanists, published Prodromus Florae Peninsulae Indiae Orientalis where they describe pongamia (growing in British gardens as an introduced species) as: "Calyx cup-shaped somewhat truncated and 5-toothed. Corolla papilionaceous glabrous. Stamens at first diadelphous at the base and apex and monadelphons about the middle, afterwards usually entirely diadelphous. Legume more or less compressed, more or less oval, with a short recurved point, 1-celled (neither contracted nor with partitions between the seeds), 1-2 seeded: valves concave on the inside, not separating naturally. Trees or twining shrubs. Leaves unequally pinnated: leaflets opposite."
A more modern description describes Millettia pinnata as a medium-sized evergreen or briefly deciduous, glabrous shrub or tree 15–25 m high, with straight or crooked trunk 50–80 cm or more in diameter and broad crown of spreading or drooping branches. Bark grey-brown, smooth or faintly vertically fissured. Branchlets hairless with pale stipule scars. Leaves alternate, imparipinnate with long slender leafstalk, hairless, pinkish-red when young, glossy dark green above and dull green with prominent veins beneath when mature. Leaflets 5-9, paired except at end, short-stalked, ovate elliptical or oblong, 5-25 x 2.5–15 cm, obtuse- acuminate at apex, rounded to cuneate at base, not toothed at the edges, slightly thickened. Inflorescence raceme-like, axillary, 6–27 cm long, bearing pairs of strongly fragrant flowers; calyx campanulate, 4–5 mm long, truncate, finely pubescent. Flower clusters at base of and shorter than leaves, to 15 cm long, slender, drooping. Flowers 2-4 together, short-stalked, pea-shaped, 15–18 mm long. Calyx campanulate, 4–5 mm long, truncate, finely pubescent; corolla white to pink, purple inside, brownish veined outside, 5- toothed, standard rounded obovate 1–2 cm long, with basal auricles, often with green central blotch and thin silky hairs on back; wings oblong, oblique, slightly adherent to obtuse keel.
Pods borne in quantities, smooth, oblique oblong to ellipsoid, 3-8 x 2-3.5 x 1-1.5 cm, flattened but slightly swollen, slightly curved with short, curved point (beaked), brown, thick-walled, thick leathery to subwoody, hard, indehiscent, 1-2 seeded, short stalked. Seed compressed ovoid or elliptical, bean-like, 1.5-2.5 x 1.2-2 x 0.8 cm, with a brittle coat long, flattened, dark brown, oily.
Robert Sweet states that the genus Pongamia comes from the Malabar region in India and is derived from the local word Pongam (most likely from the Malayalam language). Pongamia had often been misattributed to Vent. (1803), but it was preceded by "Pongam Adans. (1763)", "Galedupa Lam. (1788)", and "Pungamia Lam. (1796)" and in accordance with the 1994 Tokyo Code of the International Code of Botanical Nomenclature, the correct citation was established as "Pongamia Adans. (1763)". In 1972, S. R. Bennet, an Indian taxonomist gave the pongam a new name, Derris indica (Lamk.) Bennet, but this change has not been generally adopted. The name Derris, derived from Greek, means ‘leather covering or skin’; the specific name ‘indica’ obviously means of India. In 1981 a proposal to conserve the genus Millettia and reject the genus Pongamia was proposed in the journal Taxon and was ratified in 1988.
P. pinnata is native to humid and sub-tropic environments; common along waterways or seashores, with its roots in fresh or saltwater. It is very tolerant of saline conditions and alkalinity, and occurs naturally in lowland forest on limestone and rocky coral outcrops on the coast, along the edges of mangrove forest and along tidal streams and rivers. It is a shade bearer and can grow under the shade of other trees; it is, however, not a shade demander and grows well even with full overhead light. It is also drought resistant and well adapted to adverse climatic conditions and soil moisture conditions; prolonged drought may however kill seedlings. In its natural habitat, the species tolerates a wide temperature range. Mature trees withstand light frost, waterlogging and tolerate temperatures of up to 50 deg. C. In addition to rain, trees require a dry season of 2–6 months.
- Altitude: 0-1,400 m, Mean annual temperature: 1-16 to 27-38(50) deg. C, Mean annual rainfall: 500-2,500 mm
- Soil type: P. pinnata can grow on most soil types; best growth is found on deep well-drained sandy loams with assured moisture, but it will also grow on sandy soils and heavy swelling clay soils. It does not do well on dry sands, although it tolerates saline conditions, alkalinity and waterlogged soils. P. pinnata has been shown to tolerate high levels of heavy metals (in particular copper).
The plant is native to India, Australia and Southeast Asia. It has been naturalized in many countries of Asia, northern Africa, and the United States. Pongamia was introduced to Hawaii in the 1860s and the US Department of Agriculture received seeds from Sri Lanka, Mauritius, Egypt and India in the first two decades of the 20th century.
Despite being introduced to many new territories over the past 200 years, P. pinnata has not demonstrated any signs negative impacts as an invasive species. A comprehensive study exploring the links between biofuel production systems and invasive species conducted by the International Union for the Conservation of Nature (IUCN) concluded that P. pinnata was not invasive, stating:
"A number of oil producing trees and shrubs .... are now being promoted widely including the following ....: jatropha (Jatropha curcas), Chinese tallow tree (Triadica sebifera), neem (Azadirachta indica), olive (Olea europaea), castor oil plant (Ricinis communis), Chinese apple (Zizyphus mauritiana), moringa (Moringa pterygosperma), calotrope (Calotropis procera), giant milkweed (Calotropis gigantea), caper spurge (Euphorbia lathyris) and pongamia (Millettia pinnata). With the exception of pongamia, all of these species are known to be invasive somewhere in the world."
An invasiveness risk assessment of P. pinnata conducted by the government of Queensland, Australia found that P.pinnata "does not appear to have any significant negative impacts in Queensland". Despite having been introduced to many new regions over the past 200 years observations of self-seeding and spreading of P.pinnata are very limited. In a review of invasive woody plants of the tropics, Binggeli et al. (1998) concluded that in certain environments where P. pinnata is able to spread it "still occurs at low densities and is not considered an immediate problem". For these reasons P-pinnata is considered to be a 'low risk' plant species, suitable for controlled introduction to new regions for commercial purposes.
Where P. pinnata has been observed to spread into natural environments, simple controls have been established to minimize the risk of spreading to acceptable levels. Miami-Dade County of Florida proposed that P. pinnata "may not be planted within 500 feet of native plant communities which they have been known to invade", citing risk to pineland ecosystems but not others. Notably, no other county in the State of Florida imposes similar restrictions.
To minimize any risk of spreading, it is recommended that environmental management plans be drawn up for each introduction to ensure control of seedlings outside of orchard areas.
Products of the tree have many traditional and modern uses. The useful parts of the plant include the pods, which contain one or more seeds, leaves, bark and wood.
Oil made from the seeds, known as pongamia oil, has been used as lamp oil, in soap making, and as a lubricant for centuries. P. pinnata has the rare property of producing seeds of 25–40% lipid content of which nearly half is oleic acid. The oil has a high content of triglycerides, and its disagreeable taste and odor are due to bitter flavonoid constituents including karanjin, pongamol, tannin and karanjachromene. The seed, leaves, oil and residue of the plant are toxic and will induce nausea and vomiting if ingested.
|Flash Point||deg. C||225|
|Fire Point||deg. C||230|
|Cloud Point||deg. C||3.5|
|Pour Point||deg. C||-3|
|Boiling Point||deg. C||316|
|Copper Strip Corrosion||-||None Observed|
The residue of oil extraction is called press cake, is used as a fertiliser and as animal feed for ruminants and poultry.
Podshells, a by-product of oil extraction have a lower heating value (energy content) of 4100 kcal/kg and can be formed into pellets or briquettes and used as a substitute for charcoal for cooking and heating.
It is often used for landscaping purposes as a windbreak or for shade due to the large canopy and showy fragrant flowers. The flowers are used by gardeners as compost for plants requiring rich nutrients. The bark can be used to make twine or rope and it also yields a black gum that has historically been used to treat wounds caused by poisonous fish. The wood is said to be beautifully grained but splits easily when sawn thus relegating it to firewood, posts, and tool handles.
It can be grown in rainwater harvesting ponds up to 6 m (20 ft) in water depth without losing its greenery and remaining useful for biodiesel production.
Long used as shade tree, M. pinnata is heavily self-seeding and can spread lateral roots up to 9 m (30 ft) over its lifetime. If not managed carefully it can quickly become a weed leading some, including Miami-Dade County, to label the tree as an invasive species. However this dense network of lateral roots makes this tree ideal for controlling soil erosion and binding sand dunes.
- Smithsonian National Museum of Natural History - Proposal No. 549
- "Pongamia Factsheet" (PDF). Retrieved 2013-10-02.
- Ibáñez, M. D.; Martínez, M; Sánchez, J. J.; Fernández-Caldas, E (2003). "Reactividad cruzada de las legumbres" [Legume cross-reactivity]. Allergologia et immunopathologia (in Spanish). 31 (3): 151–61. PMID 12783766.
- Wight, Robert; Arnott, George Arnott Walker (1834). Prodromus Florae Peninsulae Indiae Orientalis: Containing Abridged Descriptions of the Plants Found in the Peninsula of British India, Arranged According to the Natural System, Volume 1. p. 262.
- Orwa, C.A. (2009). "Agroforestree Database: a tree reference and selection guide version 4.0". World Agroforestry Centre. Archived from the original (PDF) on 2009. Retrieved 11 October 2018.
- Sweet, Robert (1839). Sweet's Hortus Britannicus: Or, A Catalogue of All the Plants Indigenous Or Cultivated in the Gardens of Great Britain, Arranged According to the Natural System, with the Generic and Specific Names, English Names, Accentuation, Derivation of Generic Names (3rd ed.). p. 193.
- Plant Name Details - Leguminosae Pongamia Vent.
- Phytoremediation potential of bioenergy plants. Bauddh, Kuldeep,, Singh, Bhaskar (Environmental sciences teacher),, Korstad, John,. Singapore. ISBN 9789811030840. OCLC 980875012.
- Benjamin, Warr (11 October 2018). "Restoration of copper tailings using Pongamia pinnata". BetterWorld Energy (Zambia) Ltd. Retrieved 11 October 2018.
- Morton, J.F. (1990). "The pongam tree, unfit for Florida landscaping, has multiple practical uses in under-developed lands". Proceedings of the Florida State Horticultural Society. 103: 338–43.
- Mauremooto, John (2009). "Biofuels and Invasive Species" (PDF).
- "Invasive Plant Risk Assessment, Pongamia, Millettia pinnata syn. Pongamia pinnata" (PDF). Queensland Government. 2016.
- Bingelli, P. (1998). "An overview of invasive woody plants in the tropics". School of Agricultural and Forest Sciences Publication No. 13, University of Wales, Bangor.
- "Invasive and Banned Plants of Miami-Dade County" (PDF).
- Bobade, S.N. (2012). "Detail study on the Properties of Pongamia Pinnata (Karanja) for the Production of Biofuel" (PDF). Archived from the original (PDF) on 2012. Retrieved 11 October 2018.