Taro: The Oldest Food Crop on Earth with a 10,000 Year Culinary History
Colocasia esculenta, also known as Taro or Dasheen as well as many other vernacular names, is an important food crop, widely cultivated in a zone spanning across Asia, South East Asia and Melanesia. Its starchy root is included in the diet of about half a billion people, making it an important source of nutrition (Lebot, 2009). It is also, most probably, the oldest crop on earth with a history going back more than 10,000 years. Evidence of taro use during the early and mid-Holocene period has been found in the form of taro starch traces on tools used to process starchy food at Kuk Swamp in the Western Highlands of New Guinea (Fullager, et al, 2006).
Over the millennia, it has acquired considerable socio-cultural significance. It is a prestige crop for gifting and feasting; parts of the plant are used medicinally and it features in the folklore of Oceania and South East Asia (Onwueme, 1999).
Taxonomy, Description and the Origin of the Species
C. esculenta sits firmly in the Araceae family, a grouping of around 110 genera and over 2500 species, divided into seven subfamilies: Gymnostachyoideae, Orontioideae, Lemnoideae, Monsteriodeae, Pothoideae, Lasioideae, Zamioculcoideae and Aroideae.
Individual shoots of C. esculenta will reach a height and spread of 1.5m x 60cm (RHS, 1999) but eventual size is very much dependent on climate and cultivation factors. The morphology of Aroideae, which contains C. esculenta, includes the characteristic spadix and spathe inflorescence present in all members of this subfamily (Lebot, 2009). A spadix is a specialised form of spike inflorescence where small, sessile, individual flowers are tightly packed onto a fleshy core. Colocasia species are monoecious; the female flowers are situated at the base of the spadix with the male flowers above. The spathe, which is a large bract partially enclosing the spadix, surrounds the spadix and the space formed between these two structures provides a resting place and shelter for insect pollinators.(Lebot, 2009)
A further characteristic of Aroids, seen in C. esculenta is protogyny. This is where the female flowers become fertile and receptive before the male flowers, helping to ensure successful cross pollination.
The leaf shape is peltate in almost all genotypes and the leaf lamina can vary from 30 to over 80cm long; in part the variation is due to genotype but environmental and cultivation factors also have a significant effect on length and breadth of both lamina and petiole. Leaves are somewhat glaucous with reticulate, sometimes prominent, venation. Leaf colour can vary from pale green to deep purple with the laminae and petioles not necessarily exhibiting the same colour.
The fruit of C. esculenta is a berry, usually green in colour but may be orange or purple. The number of seeds per fruit varies with environmental and pollination factors but can be over 50 (Lebot, 2009).
The corms are the economically important part of the plant and these, like the leaves, show considerable variation due to growing conditions with the most elongated corms being characteristic of wet, paddy type conditions. Each corm consists of three parts: the skin, cortex and core. The cortex and the core consist of parenchyma tissue with fibres within the core. The skin may be smooth or fibrous and the root system is superficial and fibrous (Lebot, 2009).
History of Aroid Taxonomy
Taro was first described by Linnaeus in 1753 as two separate species which he named Arum colocasia and Arum esculentum, a classification which survived until a major revision of the Aroids by Herinrich Wilhelm Schott. Schott, arguably one of the most important plant taxonomists of the 19th Century (Reidi, 1965), dedicated a large part of his life’s work to the Araceae family (Reidi, 1965). In 1832, Schott reclassified Arum colocasia as Colocasia antiquorum and Arum esculentum as Colocasia esculentum. In 1856, in his Prodromus Synopsis Aroidearum, Schott revisited his previous classification and used Colocasia antiquorum to describe a single, polymorphic species which included previously described forms of Colocasia (Gomex-Beloz, 2006).
In 1939, the nomenclature changed again, this time to Colocasia esculenta. Albert Hill, in his paper ‘Nomenclature of the Taro and its Varieties’, chose this name as it contains the two epithets, Colocasia and Esculenta, that Linneaus used when first describing this plant (Hill, 1939). However, there is still a debate as to whether there are two distinct species:
- Colocasia esculenta
- Colocasia antiquorum (Plucknett, 1983 cited by Lebot, 2009)
or one polymorphic species with two varieties:
- Colocasia esculenta var. esculenta
- Colocasia esculenta var. antiquorum (Purseglove, 1979 cited by Gomex-Beloz, 2006)
or one species with two names:
Colocasia esculentum (L) Schott (Syn. C. antiquorum) Schott (Norman, 1992; RHS, 1999)
In the field, there are two main groups: the Eddoe, with a smaller central corm where the side cormels are eaten, and the Dasheen with a large central corm (which is eaten) and small cormels which are discarded. The Eddoe may correspond to the esculenta varieties and the Dasheen to the antiquorum, with the esculenta (Eddoe) varieties bearing the most similarity to wild forms of taro (Lebot, 2009).
In tropical regions, edible aroids, including taro, can be grown all year as they thrive in warm temperatures with high humidity. Taro does not flower or set seed easily, unless artificial gibberellic acid is applied (Onwueme, 1999) so it is usually propagated vegetatively using suckers, head-setts/huli (the top 2cm of the main corm together with the first 30cm of the petiole), small corms or corm pieces (Lebot, 2009; Onwueme, 1999).
Root formation and rapid growth occur directly after planting with corm formation being at three months. Time from planting to harvest is in the range of 5 -12 months for dryland taro and 12 -15 months for flooded taro. The average yield globally is 6.2 tonnes/hectare (Onwueme, 1999).
Pests and Diseases
Food production taro has one serious pest, the taro beetle, and one serious disease, taro leaf blight. The taro beetle (Papuana sp.) attacks the developing corms leaving holes which spoil the crop and allow rot organisms to enter. Research is taking place into finding a biological control. Taro leaf blight (Phytophthera colocasiae) can destroy a leaf lamina in 10-20 days with the disease able to cause losses of 30-50%. An integrated control programme combined with breeding resistant varieties offer the most promising ways to control the problem (Onwueme, 1999).
In the Cooking pot
Because of the high levels of oxalates, taro corms cannot be eaten raw; the acrid tasting corm causes soreness and itching on contact with the skin. However, the corms and cormels can be boiled, baked, roasted or fried as the cooking process breaks down the calcium oxalate crystals. Taro corms may be flavoured with spices, cooked or served with other foods or as a stand alone dish. They are extremely versatile and a good source of carbohydrate. The leaves also contain high levels of oxalates but are edible after cooking and can be flavoured and made into dishes. One local recipe in the Himachal Pradesh area of India is called Khatti Bhujji and made from the leaves in July-October (Kapoor, 2010).
In Cooler Climes
Colocasia esculenta is frost tender with the foliage dying down at the first frosts. The corms may stay dormant underground but, to ensure survival, can be lifted and kept dry and frost free over the winter. In the United Kingdom, it can be grown as a summer ornamental or marginal or in a heated greenhouse. Its attractive, glossy, architectural leaves have earned Colocasia esculenta the RHS Award of Garden Merit (AGM) and there are two main cultivars, developed for their attractive foliage:
- Fontanesii, with dark red to purple petioles veins and margins and
- Illustris with light green laminae but violet petioles and purple hues between the veins.
Fullager, R et al. (2006) Early and Mid Holocene tool use and Processing of Taro (Colocasia esculenta), yam (Dioscorea sp.) and other plants at Kuk Swamp in the Highlands of Papua New Guinea. Journal of Archeological Science. Vol. 33. Issue 5. pp545-614
Gomex-Beloz, A and Rivero, T. (2006) Ethnobotany Research and Applications. Vol.4 pp.101-113
Hill, A (1939) The Nomenclature of the Taro and its Varieties. Botanical Museum Leaflets. Vol. 7 No. 7 Harvard University. Cambridge, Massachussets
Kapoor, A. (2010) Indian Journal of Traditional Knowledge. Volume 9 (2) pp. 282-288
Lebot, V (2009) Tropical Root and Tuber Crops: Cassava, Sweet Potato, Yams and Aroids. Centre de Coopération en Recherche Agronomique pour le Développement, France. Printed in the UK by MPG Books Group
Norman, J (1992) Tropical Vegetable Crops. Arthur Stockwell Ltd. Ilfracombe, UK
Onwueme, I (1999) Taro Cultivation in Asia and the Pacific. Food and Agricultural Organisation (FAO) Thailand.
Plucknett, D (1983) Taxomony of the Genus Colocasia. pp 14-19 in Taro: A review of Colocasia esculenta and its potentials. Edited Wang, J. University of Hawaii, Honolulu.
Purseglove, J (1979) Tropical Crops – Moncotyledons. Longman. London
Reidi, H. (1965) Heinrich Wilheim Schott. Taxon. Vol. 14. No.7
Royal Horticultural Society ( 1999) A-Z Encyclopedia of Garden Plants. Dorling Kindersley, UK