Cyrtosperma merkusii (PROSEA)
Cyrtosperma merkusii (Hassk.) Schott
- Protologue: Oesterr. Bot. Wochenbl. 7: 61 (1857).
- Family: Araceae
- Chromosome number: 2n= 26
Cyrtosperma lasioides Griffith (1851), C. edule Schott ex Seem. (1861, " edulis "), C. chamissonis (Schott) Merrill (1914).
- Giant swamp taro, swamp taro (En)
- Malaysia: geli-geli, keladi pari, birah hutan
- Philippines: palauan (Bisaya), palau (Bisaya), galiang (Bikol)
- Thailand: kli (Malay-Pattani). Melanesia: kakake (Solomon Islands)
- Vietnam: hạt cong.
Origin and geographic distribution
The origin of C. merkusii is not known, possibly in western Malesia or in Melanesia (Solomon Islands). It is now distributed wild and cultivated from Peninsular Malaysia, throughout Malesia to Oceania, but it is absent in Sulawesi, the Moluccas and mainland Papua New Guinea. It has certainly been introduced in Micronesia and Polynesia and is now a major staple food on many islands. In Sumatra and Java it is rare, in Malaysia, Singapore, Brunei and the Philippines it is quite common.
The starchy, underground tubers of C. merkusii are edible after thorough cooking. They are peeled, cut into sections and boiled, steamed or baked and also sometimes grated or crushed and mixed with other foods such as coconut milk. Young cooked leaves are used as a vegetable. The leaves are also used as packing material (e.g. for food), as mulch and sometimes medicinally. The fibrous outer layer of the petiole can be peeled off and used in fine grades of mat weaving. In the Philippines, a decoction of the spadix is used medicinally as an emmenagogue and ecbolic. Because of its large size, C. merkusii also has ornamental value and in certain parts of Micronesia it is a highly valued prestige plant. In the Gilbert Islands, for example, pulling up an old plant to offer the large tuber to a guest is considered as the greatest honour one can pay another.
Production and international trade
In worldwide terms, C. merkusii is a minor crop, produced and traded only locally by smallholders, and no statistics are available. Where it grows in South-East Asia, it is primarily considered as an emergency or famine food although in some regions in the Philippines it is still a main staple food. In the past it played an important role in man's adaptation to inhospitable Pacific island environments. At present, it is the dominant aroid crop in Micronesia. In Polynesia and Melanesia, Colocasia esculenta (L.) Schott is the major aroid crop and Cyrtosperma merkusii kept in reserve as emergency food when taro and other crops have failed.
Per 100 g edible portion, tubers of C. merkusii contain approximately: water 63-68 g, protein 0.8-0.9 g, fat 0.1-0.2 g, carbohydrates 29-34 g, fibre 1.5 g, ash 1 g, P 28-55 mg, Ca 330-570 mg, Fe 1 mg, thiamin 0.03-0.05 mg, riboflavin 0.07-0.10 mg, niacin 0.9-1.2 mg, ascorbic acid 0.1-3 mg. The energy value ranges between 500-550 kJ/100 g. In the Philippines, the starch content of the tubers ranges between 7-23% and the starch grains are rounded to angular-rounded, (4-)11(-18)μm in size. The tubers and leaves may also contain irritating calcium oxalate raphides and some hydrocyanic acid, both of which can be removed or made inactive by cooking.
Robust to gigantic herb, up to 4 m tall, growing solitarily or in clumps. Rhizome short and slender to tuberous and very large, cylindrical, up to 2 m long and 0.6 m in diameter, sometimes globose, weighing up to 70 kg or even more, producing few to many suckers. Leaves several (6-8), sagittate, rarely hastate; petiole terete, 0.4-3 m long, up to 10 cm in diameter, usually heavily to very heavily armed with stout, conical, straight or upturned spines towards the base, but unarmed in some cultivated forms, with a prominent solid pulvinus at the apex and inside with longitudinal air ducts; blade 0.3-1.3 m × 0.8 m, sometimes armed abaxially, held horizontally to vertically with the posterior lobes down; posterior lobes usually somewhat longer than the anterior one; primary venation of the anterior lobe curvinerved in small lobes to pinnate in large lobes. Inflorescence solitary on a peduncle which is similar to but usually shorter than the petiole; spathe thick and fleshy, very variable in size, colour and shape, 2.5-30 cm long, white, yellow, green or purple, erect to deflexed to rolled back; spadix 2-24 cm long, as long as or more than half the length of the spathe, sessile or stipitate; flowers bisexual, hexamerous; ovary unilocular, (1-)2-ovulate, receptive stigma wet; stamens exserted from the tepals at male anthesis. Fruit a berry, reddish-orange, sessile, 1(-2)-seeded. Seed campylotropous, almost circular in profile to shallowly kidney-shaped, 5-11 mm long, brown, with about 3 raised, warty, longitudinal crests or sparsely and more or less irregularly warty and faintly crested.
Growth and development
C. merkusii is a slow grower and its tubers continue to increase in size and maintain their edibility for many years. Usually tubers are harvested when 3-6 years old, with a minimum of 1 and a maximum of 10 years. Older tubers begin to harden and become increasingly woody and fibrous until completely inedible. Although faster-growing cultivars also exist, their tubers are not considered to be as tasty as those from slow-growing types and the quick growers appear to be more susceptible to adverse conditions. In general, a tuber is considered mature when flowering starts.
Other botanical information
The genus Cyrtosperma Griffith comprises 11 species, all except C. merkusii , confined to New Guinea and surrounding islands. C. johnstonii (W. Bull) N.E. Brown is only known from cultivation, mainly as a gigantic ornamental, possibly also producing edible tubers but information on this is scarce. Morphologically, C. merkusii is quite variable, which is also expressed by the various existing names for it in taxonomic literature. The poise of the spathe appears to be affected by its size relative to that of the spadix. When the spathe is relatively small, its base is stretched during expansion of the inflorescence and the spathe is deflected. When it is relatively large the spathe is held erect. Cultivated forms tend to be less spiny than wild forms, some types are even unarmed; they usually also have less but larger seeds which are less marked. Locally, many cultivars are informally recognized, differing in leaf shape, colour and spininess, and in the size of the tubers. There are no registered cultivars of the cultivated forms and there is no formal classification into cultivar groups.
C. merkusii is a tropical species, occurring between latitudes 18°N (Mariana Islands) and 20°S (Cook Islands), in lowland swamp forests, open swamps or in man-made swamp pits. It requires high temperatures, and suffers chilling injury and does not tolerate temperatures below 4°C. It mostly grows at sea-level in swamps, but can be grown under year-round high rainfall as a rainfed crop up to 150 m altitude. Ideal growing conditions are natural swamplands rich in humus, about 0.5-2 m deep with slow-flowing irrigation water. C. merkusii is a very hardy plant, tolerating or withstanding drought (on atolls often because of the porosity of the soil), salt seawater sprays, brackish water and hurricanes or storms much better than most other aroid crops.
Propagation and planting
Young side shoots (suckers) and the top of the main tuber (cuttings comprising the upper 3-5 cm top of the tuber and the lower 30-50 cm of the petioles) are used as planting material. The choice is mostly a matter of local custom, but larger pieces are usually considered stronger and more vigorous. These propagules can be planted in moist or flooded soil, which is kept loose around the base of the plant so as to ensure a nicely shaped tuber. In the Gilbert Islands, in places where natural soil depth is shallow, baskets are woven around the base of the plants and filled with soil and manure as the plants grow. These plants produce large tubers if allowed to grow for several years. On atolls in the Pacific, where the soil is shallow, consisting of sand or partially decomposed coral, people dig pits or trenches down through the coral to the fresh groundwater level, and fill them with a mixture of soil, sand and green manure compost to create a suitable growing medium. Over the years, these man-made pits develop a soil of sorts in which, when supplemented with further vegetative mulches, crop residues and garbage, C. merkusii and Colocasia esculenta are grown. C. merkusii can be planted year-round, provided satisfactory growing conditions prevail. Planting depth varies, but 10-15 cm is fairly standard. Growing conditions and plant size greatly influence the spacings that are used. C. merkusii is a large plant and requires a large area, e.g. up to 1.2 m × 1.2 m in Palau and 1-3 m apart in the Philippines.
Little is known of the nutritional needs of C. merkusii but the plant responds readily to compost and organic mulch. Because C. merkusii requires 3-6 years to mature, 2-3 crops of Colocasia esculenta are often intercropped while C. merkusii is growing.
Diseases and pests
No serious disease and pest problems are known and C. merkusii is most probably more resistant than Colocasia esculenta . Dasheen mosaic virus (DMV) on the leaves and Pythium tuber rot are diseases that have been reported to cause some losses. On some islands (e.g. Mortlock Islands) rats cause serious crop losses.
Generally, cultivars are considered ready for harvesting when flowering starts; harvesting, however, occurs whenever the food is needed because the tubers can remain in the soil without loss of quality for about 10 years.
Individual tubers vary greatly in size, from an average of 2 kg in Truk and 4.5 kg in Yap, to as much as 20-50 kg or more for the giant types. The largest recorded tuber weighed about 180 kg and was grown on Ponape Island. With moderate soil fertility, annual tuber yield averages 10 t/ha, but up to 35 t/ha has been obtained in the Philippines.
Handling after harvest
If left with the top portion, harvested tubers can be stored well under cool conditions for at least 1 month. Sometimes tubers are peeled, sliced and dried in the sun; the dried parts can be stored for several months.
There are no germplasm collections. The collection of germplasm is highly recommended now that many forms are endangered. Natural seed set in Cyrtosperma is common and farmers have been known to make selections. Unfortunately, it is difficult to store Cyrtosperma seed, since it tends to be recalcitrant and must be planted soon after harvest.
There are no breeding programmes. Breeding Cyrtosperma cultivars with early maturity, low acridity, increased salt and water stress tolerance could contribute significantly to increasing production on the atolls in the Pacific. This is particularly challenging because the resources on those islands are very limited and Cyrtosperma seems well adapted to their environment.
C. merkusii is an interesting crop which has received too little scientific attention. Its ability to produce food under conditions where other crops fail (drought, floods, fresh and brackish water swamps) makes it a very useful plant in Oceania. For the regions in South-East Asia where it is not yet known, it is promising for marginal lowland areas as well, and deserves much more attention.
- Barrau, J., 1962. Les plantes alimentaires de l'Océanie, origines, distribution et usages [The edible plants of Oceania, origins, distribution and uses]. University of Aix-Marseille, Faculty of Sciences, Thesis No 71. pp. 101-104.
- Hay, A., 1988. Cyrtosperma (Araceae) and its Old World allies. Blumea 13: 427-469.
- Kay, D.E., 1973. Crop and product digest No 2. Root crops. The Tropical Products Institute, London, United Kingdom. pp. 139-143.
- O'Hair, S.K. & Asokan, M.P., 1986. Edible aroids: botany and horticulture. Horticulture Reviews 8(2): 43-99.
- Parkinson, S., 1984. The contribution of aroids in the nutrition of people in the South Pacific. In: Chandra, S. (Editor): Edible aroids. Clarendon Press, Oxford, United Kingdom. pp. 205-224.
- Thompson, S., 1982. Cyrtosperma chamissonis (Araceae): ecology, distribution, and economic importance in the South Pacific. Journal d'Agriculture Tropicale et de Botanique Appliquée 29(2): 185-203.