Nasturtium-aquaticum is from the Latin nasturtium meaning twisted nose (nasus = nose and tortus = twisted) and referring to the peppery smell/taste and aquaticum meaning growing in water.
Other Names:
Summary:
A sprawling, semi aquatic or sometimes floating perennial with long, hollow, angled stems that root at the nodes and large deeply lobed leaves and 4 petalled, white flowers nestled in clusters at the ends of stems in spring and early summer. The stalked pod is often curved, up to 20 mm long, almost at right angles to the stem and has 2 rows of seeds separated by a papery partition. It often forms dense masses in drains or ditches.
Description:
Cotyledons:
Two.
First leaves:
Leaves:
Alternate.
Stipules - None.
Petiole - Short.
Blade - Smooth, dark green, soft, up to 200 mm long by 50 mm wide with 2-5 pairs of opposite deep oval lobes or oval leaflets plus a terminal egg shaped to almost circular lobe. Edges of lobes smooth or shallowly scalloped. Tip rounded. Base squarish. Surface hairless. Edible with a sharp taste.
Stems:
Hollow, ridged, creeping. Up to several metres long and 500 mm above the water surface. Hairless or with a few sparse hairs. Stoloniferous, forms roots at the nodes.
Flower head:
Open clusters (racemes) of flowers not much longer than the leaves on slender, spreading stalks(pedicel) 8-14 mm long.
Flowers:
White, 4 petals, 4-5 mm diameter
Ovary - Superior, 2 celled.
Stigma - 1.
Sepals - 4, alternate with petals. 2-3.5 mm long
Petals - 4. White, 3-7 mm long, clawed.
Stamens - 6. (2 outer and 4 inner)
Anthers -
Fruit:
Narrow, curved or straight, upright pods without a beak, abruptly narrowed to the style. 12-20 mm long by 2-2.5 mm wide on spreading or down turned stalks, 8-14 mm long. Two rows of seeds in each half are visible through the pod. Testa or septum with about 25 polygonal depressions on each face. Mid vein scarcely or not visible.
Seeds:
Brown, spherical. Surface coarsely pitted or honeycombed and hairless.
Roots:
Fibrous at the stem nodes.
Key Characters:
Leaves glabrous or with scattered hairs, pinnatisect-lyrate. Lobes broadly elliptical, large terminal segment broadly ovate or orbicular.
Hairs simple or absent.
Flowers bisexual.
Ovary superior.
1 stigma.
Petals white, 3-4 mm long, entire, not long-acuminate, not twisted, up to twice as long as the sepals.
6 stamens, 2 outer and 4 inner.
Fruit a siliqua (long pod), linear oblong, 12-20 mm long by 2 mm wide, lacking a beak but often abruptly narrowed into the style attached to the apex.
Fruit not compressed.
Testa with about 25 polygonal depressions on each face.
Seeds in 2 rows per cell and visible through convex valves.
Adapted from John Black, Nancy Burbidge and B.L. Rye.
Biology:
Life cycle:
Perennial with its main growth over winter and spring.
Physiology:
Reproduction:
By seed, stem fragments and stems or stolons rooting at the nodes.
Flowering times:
November to February in New Zealand.
October to December in WA.
September to April in SA.
Seed Biology and Germination:
Vegetative Propagules:
Stems and fragments form roots at the nodes.
Hybrids:
Allelopathy:
Population Dynamics and Dispersal:
Spread by seed, stem fragments and stems or stolons rooting at the nodes.
Origin and History:
Europe, North Africa, Western Asia, North and South America, New Zealand.
Distribution:
ACT, NSW, NT, QLD, SA, TAS, VIC, WA.
Habitats:
Climate:
Temperate
Soil:
Winter wet depressions, slow moving rivers, drains and ditches.
Plant Associations:
Water weeds.
Significance:
Beneficial:
Edible vegetable. Contains vitamin A and is a rich source of vitamin C.
Detrimental:
Weed of waterways.
May block drains and cause local flooding.
Toxicity:
May contain toxins when grown in polluted waterways.
Wild plants may have liver fluke and should not be eaten.
Symptoms:
Treatment:
Legislation:
None.
Management and Control:
Start control program at the top of the water way to reduce re infestation.
Thresholds:
Eradication strategies:
Spray a mixture of 5 g Eclipse® plus 250 mL spray oil in 100 L water on plants until just wet in spring before pod set each year. In drains that are dry at the time of spraying, diflufenican may be useful to reduce seedling establishment.
Most of the Brassicaceae weeds have dormant seeds that continue to germinate throughout the season and for several years. They often mature and set seed very quickly. Manual removal is effective but must be done at least every 8-10 weeks. Once pods are formed, seed will often mature even if the plant has been uprooted. Soil disturbance often leads to a flush of seedlings.
Many are somewhat unpalatable, so grazing only offers partial control. They often flourish in undergrazed, sunny areas.
In bushland situations, fairly selective control can be achieved with 100 mL spray oil plus 0.1 g Eclipse® or 0.5 g Logran® in 10 L water. 5 mL Brodal® is often added to this mix to provide residual control of seedlings. Spray the plants until just wet from the seedling stage up to pod formation.
Isolated plants should be removed manually and burnt if flowering or seeding and a 10 m buffer area sprayed with 10 mL Brodal® in 10 L water.
500 mL/ha of glyphosate(450g/L) can be used at flowering to reduce the seed set of most species on roadsides without causing significant damage to most native plants.
Wick application with 1 part glyphosate(450g/L) in 2 parts water or overall spraying with 100 mL glyphosate(450g/L) in 10 L water provides reasonable control of most species though Wild Radish tends to regrow.
Herbicide resistance:
None reported.
Biological Control:
Related plants:
Forest Bitter-cress (Rorippa gigantea)
One-rowed Watercress (Rorippa microphylla) has darker or bronzed leaves, larger flowers, longer fruit and the seeds are in one row.
Yellow Cress (Rorippa palustris)
Plants of similar appearance:
Water Celery (Apium nodiflorum)
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P136. Photo.
Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P184.
Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney).
Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Volume . P. Diagram.
Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P120. Photo.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). #862.4.
Marchant et al (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P168.
Roy, B., Popay, I., Champion, P., James, T. and Rahman, A. (1998). An Illustrated Guide to Common Weeds of New Zealand. (New Zealand Plant Protection Society). P104. Photo
Acknowledgments:
Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.