Alocasia macrorrhizos (elephant ear taro)
Leaf of Alocasia macrorrhizos
Alocasia macrorrhizos (L.) G. Don
elephant ear taro, giant taro
Not of conservation concern.
Tropical humid forest. Commonly found growing around human settlements.
Food, medicine, ornamental.
The rhizomes (swollen underground stems) contain stinging calcium oxalate crystals.
About this species
Elephant ear taro is a giant plant with distinctive leaves and is valued as an ornamental. The swollen underground stems are used for food and animal fodder, and the roots and leaves are used medicinally in some countries. For example, in Hawaii, it has been used to treat digestive complaints, as a topical dressing for burns, and as a love charm. In the Philippines, the leaf stalks have been used to relieve toothache and on Java the roots and leaves have been used to relieve pain and redness. The rhizomes contain an anti-fungal protein called alocasin.
Geography and distribution
Alocasia macrorrhizos is found throughout IndoMalesia and Oceania. It is not clear where, if anywhere, this species occurs truly wild. It has evidently been distributed widely in tropical Asia in prehistoric times as a subsistence crop and is now pantropical by introduction as an ornamental.
Elephant ear taro is a massive aroid with a spectacular cluster of upwardly pointing, arrow-shaped leaf blades which can reach one metre in length. The flowering parts are often inconspicuous, and are partly concealed by the floral bract. This bends back and then falls off at maturity though, to reveal a spike of red berries, each of which contains several pale brown seeds.
Elephant ear taro is a massive herb, forming a thick erect trunk in large plants and reaching four metres in height. The leaves are held erect, with petioles (leaf stalks) up to 130 cm long. The leaves are stout, with sheathing in the lower part. The leaf blades are arrow-shaped, bluntly triangular in general outline with somewhat rounded basal lobes. There are about nine main veins, diverging at an angle of about 60 degrees.
The inflorescences (flower stalks) occur in pairs amongst the leaf bases, preceded by a cataphyll (scale leaf). The spathe (floral bract) is about 13 to 35 cm long, constricted about 1/6 of the way from the base, with the lower part folded into a green tube. The limb is oblong, pale yellow, cowl-like when in flower, then bending back and deciduous. The spadix (flower spike) is slightly shorter than the spathe. The lowermost 1 to 2 cm of the spadix is female and covered with about 30 pistils (female parts). Each pistil consists of a pale green ovary with a yellow 3 to 5 -lobed stigma sitting directly on it. Above the female flowers there is a zone with about four whorls of white sterile organs corresponding in position to the spathe constriction. The next floral zone is male, covered with tightly packed white rhomboid to hexagonal male flowers. At the tip of the spadix is a yellowish appendix, which is at least half the spadix length and covered with tiny irregular furrows.
The fruit is a few-seeded red berry, which when ripe is exposed by the recurving segments of the lower spathe tube, which detaches on maturity. Each berry has several pale brown seeds about 4 mm in diameter.
The rhizomes (swollen underground stems) of Alocasia macrorrhizos are traditionally eaten as a starchy food throughout IndoMalesia and Oceania. It is thought to have once been a major staple food in Micronesia that became extinct there prior to the introduction of related taro species (for example Colocasia esculenta). The rhizomes are used for animal feed and famine food for people. They require prolonged preparation and boiling or roasting to rid them of stinging calcium oxalate crystals.
Today, Alocasia macrorrhizos is a popular ornamental plant grown for its large foliage and striking aroid inflorescences. It has also shown promise in sewerage treatment, as it grows rapidly in wetland conditions and has a propensity to accumulate metal contaminants such as zinc.
Akana, A. (1922). Hawaiian Herbs of Medicinal Value. Pacific Book House, Honolulu.
Hay, A. & Wise, R. (1991). The genus Alocasia (Araceae) in Australasia. Blumea. 35: 499-545 [for descriptive and geographical information]
Hay, A. (1998). The genus Alocasia (Araceae-Colocasieae) in West Malesia and Sulawesi. Gardens Bull. Singapore. 50: 221-334. [for descriptive and geographical information]
Hay, A. (1999). The genus Alocasia (Araceae-Colocasieae) in the Philippines. Gardens Bull. Singapore. 51: 1 - 41.
Ivancic, A., Roupsard, O., Garcia, J.Q., Lebot, V., Pochyla, V. & Okpul, T. (2005). Thermogenic flowering of the giant taro (Alocasia macrorrhizos, Araceae). Canadian Journal of Botany 83: 647 – 655 [for flowering behaviour]
Lee, R.A., Balick, M.J., Ling, D.L., Sohl, F., Brosi, B.J. & Raynor, W., (2001). Cultural dynamism and change: an example from the Federated States of Micronesia. Economic Botany 55: 9-13.
Quisumbing, E. (1978). Medicinal Plants of the Philippines. Katha, Quezon City.
Samake, M., Wu, Q.-T., Mo, C.-H-. & Morel, J.-L. (2004). Plants grown on sewage sludge in South China and its relevance to sludge stabilization and metal removal. Journal of Environmental Sciences 15: 622-627.
Kew Science Editor: Simon Mayo
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