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Ludwigia helminthorrhiza |
| by Claus Christensen |
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Ludwigia is a very variable genus that contains many aquatic forms. Ludwigia is found all over the world and they have evolved the most peculiar structures, often closely adapted to the modelling environment. Consequently, due to the many different vegetative forms taxonomic misplace within the Ludwigia genus is rather common. Ludwigia helminthorrhiza is found widespread over the northern parts of South America and in Central America. In the wild, it develops floating carpets along the banks of rivers and in ponds and lakes. Ludwigia helminthorrhiza is an amphibious plant that resembles most other herbaceous plants when it grows on swamps. Growing as a floating plant, however, Ludwigia helminthorrhiza develops spongy air-filled roots from the axils that helps balance the plant on the water surface. These white buoyant roots cause a very characteristic and peculiar appearance. In addition, Ludwigia helminthorrhiza develops normal roots that hang down from the stalk into the water. These roots occasionally reach the bottom and prevent the plant to drift down the river in the wild. The plant spreads quickly from adventitious shoots but if the stand becomes too dense it sets vertical shoots which do not produce the peculiar spongy air-filled roots.
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Ludwigia helminthorrhiza can grow completely submerged but it tends to seek back to the water surface. Growing submerged the plant soon develops the spongy air-filled roots which seem to force the plant back to the water surface even faster and submerged leaves are lost, but contact to the sediment is usually maintained as the plant probably obtains nutrients from the much richer substrate in the bottom. The plant is quite light demanding but it thrives in well-illuminated aquaria with for example high pressure metal halogen lamps. At very high light the plant develops red leaves and the growth becomes more compact due to shorter internodes. The leaves often turn yellowish at nutrient deficiency and it is specially sensitive to micro-nutrient deficiency. It is very temperature tolerant and it is useful as summer pond plant in the temperate gardens, too. Of course, Ludwigia helminthorrhiza is most suitable for open aquaria but it is also quite useful in traditional aquaria due to the ornamental effect of the roots and many fishes thrive much better when they can seek shelter under floating plants. Likewise, it is suitable as spawning substrate for some fish.
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