If you go to your favourite plant nursery or garden centre in your hometown, chances are that you find giant taro on display, for sale as a magnificent, shade-tolerant plant for larger gardens in mild climates. But if you go to a farmer’s market in Bangladesh, the Philippines, or in Tonga, you might find the stem of the same plant species for sale as a popular food crop.
Giant taro (Alocasia macrorrhizos (L.) G.Don), sometimes also called giant alocasia or giant elephant ear taro, belongs to the aroid (Araceae) family, which consists of 107 genera with over 3,700 species distributed worldwide. The majority of aroids are climbers and epiphytes of tropical rainforests, and many species are associated with aquatic or semi-aquatic environments. Most crop species in the Araceae family, among them the ‘normal’ taro Colocasia esculenta, thrive in moist to flooded conditions and are among the most shade tolerant of terrestrial food crops. The genus Alocasia comprises more than 110 species, which grow primarily in the understorey of perhumid, subtropical and tropical lowland forests. Growth forms range from small herbaceous to thick-stemmed massive plants with huge leaves. The genus is distributed across tropical Asia, Southeast Asia, and the Malesian region, with one species in the genus being native to Australia.
Alocasia macrorrhizos was first described in 1839. In cultivation, the above-ground stem can be up to 1 m (sometimes even 3 m or more) long and 20 cm in diameter. The plants keep growing, and when an individual plant becomes too heavy to support its own weight, the stem falls on the ground and thence is decumbent but the plant continues to grow from the tip or lateral buds. The broadly sagittate leaves, which sometimes can reach a size of 1-2 meters, are bluntly triangular in outline, indistinctly leathery and showcase a prominent secondary venation. Like many other members of the Araceae family, A. macrorrhizos is an allogamous species and pollinated by insects. The inflorescences are relatively large and sit in clusters. The upper part of the spathe is pale yellow, membranous, oblong, and hood-forming, and it falls soon after anthesis. The spadix is divided into several distinct parts. The female (= carpellate) part is at the base of the spadix while the male (= staminate) part is higher up. These two zones are separated by a small, sterile zone in the centre of the spadix. The spadix ends in a sterile appendix at its top. The main purpose of this appendix is to release odorous substances. In order to do that, the male part of the spadix and this sterile appendix at the top produce heat, which is a very energy-demanding process for the plant. One scientific study measured temperatures of > 25° C above the ambient temperature and with a recorded maximum at 47.4° C, lasting for almost two days. The fruits (berries) are ovoid, scarlet and about 1 cm long. Seeds develop only rarely.
A. macrorrhizos was prehistorically distributed widely in tropical Asia and the South Pacific region and was used as a subsistence crop in times of famine. In the Philippines, South Asia and many Pacific island countries and territories (to name a few, Samoa, Fiji, Tokelau, Tonga, Tuvalu, Wallis and Futuna, Papua New Guinea, the Solomon Islands, and Vanuatu), it has been cultivated for at least 3,000 years as a starch food crop, often as part of traditional agroforestry systems, together with banana, cassava, coconut, kava, sweet potato, tannia, taro and yams. In the South Pacific countries, the crop is harvested after usually 12 to 24 months and can be harvested all year round. As it can withstand drought periods better than other aroids and can grow in different soil types, it is often considered an important resource during periods of food scarcity. The stem is roasted, baked or boiled and eaten as a source of carbohydrates. In India and Bangladesh, the stem tuber is peeled, cut into pieces and eaten as a vegetable after cooking, usually in curries or stews. In Fiji, the leaves are used to cover the lovo, the traditional earth oven.
Stems of wild plants are not consumed as food because of an extremely high concentration of calcium oxalate crystals which cause considerable irritation and swelling of affected tissues. But even in its cultivated form, giant taro needs to be cooked or otherwise processed to render it palatable. In the literature, there is a degree of uncertainty whether (and if, where) truly wild populations exist. If not in cultivation, A. macrorrhizos is often found in roadside ditches and margins of wet fields. Also, feral plants that escaped from cultivation can be found, which in their appearance resemble wild plants.
There is a relatively large body of pharmaceutical literature on medicinal use and medical effects of secondary metabolites of A. macrorrhizos. The crop is widely used in folk medicine for a range of different conditions and diseases. It is traditionally used for the treatment of diabetes, pus in the ears, jaundice, snake bites, and constipation. In Malaysia, it is used to treat cough and toothache. In India, Bangladesh, and parts of Indonesia, it is used as an analgesic medication to alleviate pain in the stomach, head, and rheumatoid arthritis. In Vietnam, A. macrorrhizos is used to treat inflammation, eczema, and abscess. In the Philippines, it is traditionally used to cure rheumatism, snake bites and toothache.
It is maybe surprising that despite its wide and multiple uses, genetic samples of A. macrorrhizos which are available to plant breeders or for species conservation purposes are very rare. My own search in online databases and the scientific literature showed a total of only 59 accessible samples held in nine gene banks worldwide.
If my blog made you curious to learn more about giant taro, I would like to direct you to a recent scientific review, that I have co-authored jointly with Filippo Guzzon. Please follow this link to the open access publication.
Plants worldwide 