Synonyms - Hydrocotyle natans
Family: Apiaceae or AraliaceaeNames:
Floating marsh-pennywort, floating pennywort , greater water pennywort, marsh pennywort, pennywort, water-pennywort.
Summary:A hairless, scrambling, semi aquatic weed with petioles attached to the centre of circular leaves. It has stems running along or just under the ground with erect lateral stems bearing a terminal clusters of flowers.
Leaves:Alternate leaves are emergent or floating and sit above the horizontal stem on fleshly petioles up to 40 cm long. The leaves are not peltate.
Stipules - paper like, 2-4 mm long
Petiole - 100-400 mm long, thickened towards the base,.
Blade - Circular to kidney shaped with an indented (cordate) base, 20-45 (100) by 25-55 (180) mm. and usually broader than long. Shallowly or deeply incised into (3)7-11 rounded, crenate or lobulate subequal lobes.
Shiny, somewhat fleshy. Tip rounded, sides shallowly lobed and the lobes are scalloped (crenate), base indented.
Stems:Prostrate, low lying rooting at the nodes and bearing a leaf or a flowering stem with a terminal inflorescence.
Stems float in the water or creep onto the shore and the plants root freely from nodes at about 30-100 mm intervals.
Flower stem - may root at the nodes. Up to 200 mm long.
Flower head:Simple, small umbel 3-4 mm across.
The inflorescence is borne on a leafless stalk (peduncle), 10-60 mm in length and remaining shorter than the petioles so is held just below the leaves. The flowers are on short. 1 mm long pedicels and there are 5 to 10 in a small umbel.
The bracts are 0.5 mm long and entire.
Flowers:The flowers are hermaphrodite and white.
Ovary - Inferior, circular, 1 mm diameter, hairless, two-lobed and has 2 styles.
Sepals - None
Petals - White. 5 unconnected petals.
Stamens - 5
Fruit:Schizocarp fruits (capsules) are brownish, nearly round and flat, 2-3.5 mm in diameter with faint ribs and divided into two halves, each with a small persistent stalk
Roots:Stolons with fibrous roots at the nodes. Fruiting branches may root at the nodes.
Key Characters:Van de Wiel et al. (2009) developed a DNA barcode that discriminates against closely related species.
Aquatic, stoloniferous herb, growing in water with emergent and submerged leaves.
Leave reniform to circular and cordate with a deep sinus 20-45 x 25-55 mm.
Non peltate leaves.
Stems not winged.
Fruit broader than long, transversely elliptic.
Vegetative growth can be very rapid, with floating mats extending up to 200 mm per day. In Central Europe, the growth rate is highest in the summer months. Starting from small plants or fragments, plants start growing slowly in spring as soon as the ice melts. Small leaves (up to 10 cm2) are formed that float on the water surface for the most part. With increasing temperature, photoperiod and light intensity, the leaves become larger and reach a height of up to 400 mm above the water. The hermaphrodite plants flower and fruit between May and October as the stands become denser. With temperature and light availability decreasing in autumn, plants develop smaller fresh leaves. At this time, plants have both floating and submerged leaves. Most of the leaves die off as night frosts set in. Floating leaves die when enclosed in ice, but submerged stems and leaves survive the winter. From the persisting small submerged plants and leafless stolons, plants grow out again in spring.
Reproduction:Spread by stem fragments that root at the nodes. Up to 90% of stem fragments 10 mm in length and with only one node, with or without leaves, regenerate within one week. Single leaves and internode fragments do not regenerate.
Spread by seed has not been documented.
Spread by birds, water flows and dumping of waste.
Flowering times:December to February in Western Australia
Flowers throughout the year with a flush in October to February elsewhere.
Seed Biology and Germination:
Vegetative Propagules:Forms roots at the nodes of stems and stem fragments.
Allelopathy:Ecology, Population Dynamics and Dispersal:
Origin and History:Native to North America, Middle America, South America, Yemen and Tropical Africa or Europe.
Courtesy Australia's Virtual Herbarium.
Courtesy Australia's Virtual Herbarium.
Habitats:Grows in stagnant and slowly running water. It colonizes the shallow parts and banks of rivers, streams, ditches, weirs, ponds, lakes and freshwater marshes. It tolerates tidal conditions or strong irregular water-level variations and grows on all types of soil, including peat. It will also grow on drained soils. Once established, it is able to spread into deeper water by forming extensive floating mats. This growth form allows it to cope with frequent water-level changes. It grows best at high-nutrient sites, tolerating turbid water and organic pollution. Establishment also occurs on banks which remain barren of any other vegetation. Although highly eutrophic, base-rich sites may be especially susceptible, invasive behaviour also occurs in more nutrient-poor and even acid conditions. It prefers sunny conditions and reaches maximum photosynthetic rates of up to up to 18 ìmol CO2 m-2 s-1 at 25-350C and a light saturation of ~ 800 ìmol photons m-2 s-1.
It tolerates very cold winters, but frost causes emergent parts to die back with submerged parts persisting.
Soil:Sandy or waterlogged areas. Can survive under water or floating while still attached to the shore.
It has some uses in water treatment as it accumulates heavy metals.
Detrimental:Competes with many native plant species, including littoral marsh plants, such as species of Carex, Juncus, Myosotis and Rorippa, as well as submerged aquatic plants. These are overgrown and shaded out by the extensive beds or floating carpets. Species richness of native aquatic plants may be reduced by more than 50% and submerged species may even disappear entirely (Nijs et al. 2009).
Floating mats affect the penetration of light available for photosynthesis, reduce oxygen levels in the water column which can result in fish mortality and influence invertebrate life (EPPO 2009, Stiers et al. 2009). If leading to sediment anoxia, the release of nutrients and potentially toxic substances can be enhanced. Rapid biomass accumulation fuels decomposition processes, alters the composition of the bottom substrate and expedites the infilling of shallow standing waters. In flowing waters, drainage is impeded and siltation increases with heavy infestations.
May cause flooding
The use of harvested plants as fodder for live stock (Leeflang 2008) or for energy production does not appear to be worthwhile.
The Netherlands and Belgium spend 3 million Euros a year on control.
Toxicity:Not recorded as toxic.
Legislation:Declared plant in Australia and under eradication.
Management and Control:More susceptible to 2,4-D amine and somewhat resistant to glyphosate in overall sprays in the field (Newman & Dawson, 1999). However, mechanical removal followed by 360 gai/ha glyphosate provided good control in other studies (Ruiz-Avila & Klemm, 1996).
Several rounds of manual removal are required for adequate control.
Eradication strategies:Spray with 5 L/ha 2,4-D amine500 in summer then mechanically remove plants 4 weeks later then spray with 2 L/ha glyphosate aquatic360 4 weeks later.
The use of 2,4-D ester800 is worth trialling as the volatility may provide higher levels of control of fragments that don't receive a direct dose of herbicide.
Biological Control:None at present but research is continuing overseas.
Unlikely to be used in Australia while eradication is the goal.
Related plants:Pennywort (Hydrocotyle bonariensis) has circular peltate leaves (the petiole attaches to the middle of the leaf) and it holds its larger compound inflorescence higher just above the leaves in summer.
Stinking pennywort (Hydrocotyle laxiflora) native to eastern Australia.
Pennyweed (Hydrocotyle tripartita) native to eastern Australia.
There are several native Hydrocotyle species
Plants of similar appearance:Frog's Mouth ()
References:Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).
Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (2007). Western Weeds. A guide to the weeds of Western Australia. (Second Edition). Plant Protection Society of Western Australia, Perth, Western Australia. P82. Photo.
Hussner, A., Denys, L., van Valkenburg, J., 2012. NOBANIS - Invasive Alien Species Fact Sheet - Hydrocotyle ranunculoides.
Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). P90. #513.5.
Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P510.
Newman, J.R., Dawson, F.H., 1999. Ecology, distribution and chemical control of Hydrocotyle ranunculoides in the U.K. Hydrobiologia 415, 295-298.
Newman, J.R., Duenas, M.A., 2010. Information sheet: control of floating pennywort (Hydrocotyle ranunculoides).
Paczkowska, G. and Chapman, A. (2000). The Western Australia flora: a descriptive catalogue. (Wildflower Society of Western Australia (Inc), the Western Australian Herbarium, CALM and the Botanic Gardens & Parks Authority). P147.
Randall, J.M. and Marinelli, J. (1996) Invasive Plants. (Brooklyn Botanic Gardens Inc. Brooklyn). P. Photo.
Ruiz-Avila, R.J., Klemm, V.V., 1966. Management of Hydrocotyle ranunculoides L.f., an aquatic invasive weed of urban waterways in Western Australia. Hydrobiologia 340, 187-190.
van de Wiel, C.C.., van der Schoot, J., van Valkenburg, J.L.C.H., Duistermaat, H., Smulders, M.J.M., 2009. DNA barcoding discriminates the noxious invasive plant species, floating pennywort (Hydrocotyle ranunculoides L.f.), from non-invasive relatives. Molecular Ecology Resources 9, 1086-1091.
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