Taxonomic name: Limnocharis flava (L.) (Buchenau, 1903)
Synonyms: Limnocharis emarginata H.B. & K.Pl. aequin. 1(1807)116, t.34; Micheli. In DC. Mon. Phan.3 (1881) 89., Alisma flava Linn. Sp. Pl.1 (1753) 343., Damasonium flavum (L.) Mill. Gard. Dict. ed. 8. (1768), Limnocharis laforesti Duchas. ex Griseb. Bonplandia 6:11 (1858), Limnocharis mattogrossensis O. Ktze. Rev. Gen. 3˛:324 (1893), Limnocharis plumieri Rich., Mem. Mus. Hist. Nat. Paris 1 (1815) 370, t.19, f.11, t.20
Common names: cebolla de chucho (Spanish), cu neo (Vietnamese), kalmi (Bangla), kengkong (Bangla), keo neo (Vietnamese), limnocharis, manja payal (Malayalam), paku rawan (Malay), sawah-flower rush (English), sawah-lettuce (English), velvetleaf (English), yellow bur-head (English)
Organism type: aquatic plant Limnocharis flava is a clump-forming, emergent aquatic plant that is native to the American continent. The Greek words "Limno" and "charis" mean "pond" and "grace", respectively. The attractiveness of this plant, with its inflourescenes of pale yellow flowers, has lead to its cultivation in gardens, which has facilitated its dispersal to new locations. Description
L. flava has triangular-shaped leaf and flower stalks and produces 'octopus-like' inflorescences consisting of up to 15 three-lobed yellow flowers. Its fruits are spherical and made up of cresent shaped segments that eventually split off, carried by water currents to disperse seeds to new locations (CRC for Australian Weed Management, 2003). The botanical specifics are noted as follows. It is glabrous (lacks hairs and is smooth), scapigerous (produces leafless flowering stalks) and lactiferous (contains a milky substance). It has a short stout rhizome (which measures about 3cm long and 3cm in diameter) and numerous fibrous roots. The leaves are erect, sheathing and curvinerved, and rise in clusters above the water. The petioles are thick, triangular , 90cm long and contain numerous lacunae (air spaces). The leaf sheaths narrow towards the top and the leaf blade is papery, light green, variable in shape (rounded, ovate or broad elliptic) and 6 - 20cm long (and almost as equally wide). The leaf apex is generally apiculate with a small hydathode at the tip; the leaf base is cuneate to repand-cordate; the leaf margin is undulate. There are four to six pairs of main nerves and a marginal one (sub parallel and converging towards apices), numerous secondary nerves (parallel to each other and nearly perpendicular to the midrib) and dense fine reticulations. There are about one to four peduncles (flower stalks), which are axillary, erect, triangular, flattened at the base and 120cm long. Penduncles bear, at the apex, a cluster of flowers, a ramet (vegetative plant) or both. Inflorescences are umbellate (consisting of flowers springing from a common center and arranged in a cluster), with between two to 15 flowers supported by an involucre of bracts; sometimes one or two leaves are present between the flowers. The bracts are roundish to broad-elliptic with (usually) emarginated tops. The flowers are pedicelled, actinomorphic, hermaphrodite and 2 - 4cm in diameter. The pedicel (stalk of a flower in an inflorescence) is 2 - 7cm long (3-gonous, 3-winged above, enlarging upwards and much elongated in fruit). The perianth is 2-seriate. The three sepals are persistent, imbricate (overlapping), green, obtuse in shape, 1.5 - 2cm long by 1 - 1.5cm wide, and enlarge and enclose the fruit. The three petals are pale yellow with a darker base, thin, caduceus (tend to fall off early), imbricate and broad-ovate to orbicular in shape with a rounded apex and are 2 - 3 longcm by 1 - 2cm wide. There are numerous stamens surrounded by a whorl of staminoides (filaments flattened, free, anthers basifixed, 2-celled, dehiscing longitudinally). There are 15 to 20 carpels (verticillate, laterally compressed, free, densely set, seemingly forming one superior ovary, ovules many, placentation superficial, styles wanting, stigmas sessile). The fruit are composed of fruitlets (as many as there are carpels) which are scarcely cohering, semicircular, membranous, opening along the adaxial (inner or ventral) side and having a thick abaxial (outer or dorsal) wall. There are numerous very small, horseshoe-shaped seeds, which are densly crowded together. The testa (hard outer covering or integument of a seed) is brown and spongy. Endosperm: 0 (Abhilash, 2004). Occurs in:
agricultural areas, ruderal/disturbed, wetlands Habitat description
L. flava inhabits shallow swamps, ditches, pools and wet rice fields, occurring usually in stagnant fresh water (Abhilash, 2004). General impacts
If allowed to grow unchecked, L. flava may become a very invasive environmental weed of streams and wetlands. It has become a serious weed in rice fields, irrigation canals and wetlands in South-East Asia (Waterhouse, 2003). Clumps of the weed provide a congenial breeding sites for disease-vectors, including mosquitoes, which encourages the spread of diseases such as Japan fever and dengue fever (Abhilash, 2004). Notes
The Chromosome number for this species is 2n = 20 (Sunder Rao, 1953). Geographical range
Native range: America (North Western Mexico, Nicaragua, Costa Rica, Panama, Cuba, Haiti, Dominican Republic, Windward Islands, Colombia, Venezuela, Ecuador, West Indies, Peru and Brazil).
Known introduced range: Southeast Asia (Malaysia, Indonesia, Thailand, South Myanmar, Srilanka, India and Vietnam), and Australia (Abhilash, 2004; Ogle et al. 2001; Waterhouse, 2003). Introduction pathways to new locations
Agriculture: It is thought that the introduction of L. flava into India may have been due to contaminated imports of rice from rice paddies in South East Asia infested with the weed (Abhilash, 2004). As well as unintentional spread of the seed via agricultural imports its use and cultivation as a food source may result in intentional spread of the plant into new countries. The latter is thought to be the cause of its spread from Java to Papua (Waterhouse, 2003).
For ornamental purposes: The plant was introduced into Singapore for ornamental purposes (Corlett, 1988). It is also used as an ornamental plant in aquaria and pools in North America; this practice encourages the establishment of the weed (Abhilash, 2004).
Other: Movement of L. flava from Irian Jaya (Papua) to Papua New Guinea as a source of food is inevitable (if it isn’t there already). This is also thought to be the reason for its introduction into Papua from Java (Waterhouse, 2003).
Taken to botanical garden/zoo: In the late 19th century L. flava was cultivated in the Bogor Botanic Gardens and Peradeniya Botanic Gardens, precipitating its spread in Indonesia and Sri Lanka, repectively (Senartana, 1940; van Steenis, 1954).
Local dispersal methods
Agriculture (local): Seeds may be transported into uninfected areas when cereals are transported from a contaminated field. The plant is cultivated in Java (Indonesia) for a local food source, an activity which may facilitate its spread in the region (Abhilash, 2004).
Hikers' clothes/boots: Seeds may be dispersed by man and his impediments (Abhilash, 2004).
Natural dispersal (local): Although seed production is prolific, the plant is also able to propagate vegetatively (clonally). Vegetative plantlets (known as ramets) either take root in the mud below the mother plant or break off and float away to new locations (CRC for Australian Weed Management, 2003).
On animals (local): Seeds may stick to and be dispersed by birds frequenting the fields (Abhilash, 2004).
Other (local): The weed is reported to be used as pig or cattle fodder (in Sumatra), and as green crop manure for fertilising paddies; both activities encourage the establishment of the weed as a pest (Abhilash, 2004).
People foraging: In the Mekong Delta (in Vietnam) the plant is collected (but not specifically cultivated) and sold in local markets and by boat vegetable vendors (Ogle et al. 2001). Presumably, this encourages the spread of the plant through the movement of seeds and vegetative material.
Water currents: L. flava reproduces mainly by the production of seeds. Seeds are dispersed via the production of fruitlets, which are buoyant and carried by water to new localities, dispersing seeds along the way. Fruiting takes place throughout the year, with a single fruit producing about 1000 seeds and a single plant producing about 1000 fruits per year (Senartana, 1940). Management information
Strategies employed to control L. flava should emphasis public education. The effects of the invasive weed should be outlined, and the practices necessary for limiting its spread should be made clear. For example, plants should be uprooted and burnt (or deep-buried) to prevent them from re-establishing and the plants should be (preferably) removed before the weed flowers and sheds its seeds. An increased understanding of the life cycle of the weed should be attempted through ecological studies; these may highlight the most vulnerable stages of the life cycle and eventually lead to more effective control measures. The use of the plant as a leafy vegetable, green manure, medicine, or in other applications should be documented so that the social and economic factors contributing to the spread of the plant can be addressed (and potentially reduced).Preventative measures: In general, early detection of any invasive weed species provides the best opportunity for intervention. This is because eradication or control programs implimented at an early stage of an invasion have a higher chance of success and are more cost-efficient. To encourage early detection, the Northern Australian Quarantine Strategy (NAQS - a sub-program of the Australian Quarantine and Inspection Service) have undertaken a survey of the distribution of known weeds (and the occurance of new weeds) in northern Australia. Field surveys such as this provide current distribution records of weeds in an area and are necessary for fast detection of a new invasive weed. Detection is also hindered by the under-representation of weeds in herbaria (collections of preserved plants). This is due to the fact that botanical collectors rarely document introduced species. To address this, botanists working under the NAQS collect naturalised species in addition to native taxa, providing an opportunity to consolidate knowledge of weed flora in the region (considered to be essential for prioritising weed management in any area) (Waterhouse, 2003). Reproduction
Flowering and fruiting takes place throughout the year, with a single fruit producing about 1000 seeds, and a single plant producing about 1000 fruits per year (Senartana, 1940). The flowers open in the morning and close by mid-day, after which the stamens and petals disintegrate into a mucilaginous mass (van Steenis, 1954). There are no known pollinators for the plant in either South America or South east Asia. Spherical shaped fruit develops and ripens, opening along the adaxial (inner) wall; this is due to the thick curving abaxial (outer) wall. Each fruit consists of individual cresent shaped segments, known as fruitlets; the fruit and fruitlets may float for several days, scattering the numerous tiny seeds as they float downstream. The plant may also propagate clonally. A vegetative plantlet, known as a ramet, develops in the centre of an inflorescence. After the fruit has fallen, the penduncle (stalk of the inflorescence) bends over and the ramet eventually reaches the surface of the water. It then sends out its own rhizome and roots, which take root in the mud below. Alternatively, ramets may break off and float away, forming new infestations downstream (Abhilash, 2004; CRC for Australian Weed Management, 2003). Lifecycle stages
Where moisture is present year-round L. flava is a perennial herb; in ephemeral water-bodies and sites with pronounced dry seasons it is an annual (van Steenis, 1954). Reviewed by: Abhilash, P.C, School of Environmental Sciences, Mahatma Gandhi University, Kottayam, Kerala, India.
Compiled by: Abhilash, P.C, School of Environmental Sciences, Mahatma Gandhi University, Kottayam, Kerala, India & IUCN/SSC Invasive Species Specialist Group (ISSG)
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Last Modified: Sunday, 26 June 2005
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