Common Names: Pygmy chain sword
Native Distribution: North, Central, and South America
Aquarium Placement: Foreground
Requirements: Undemanding and very adaptable to many environments
Helanthium tenellum, the pygmy chain sword, can be found as a bog plant from the northern United States through Central America to Paraguay, South America. Long known both botanically and in the aquarium hobby as Echinodorus tenellus, it is now classified as a Helanthiumspecies. These plants were assigned to the subgenus Helanthium by Haynes and Holm-Nielsen in 1994. In 2007, the subgenus was made a full and separate genus by Samuli Lehtonen and Leena Myllys, based on cladistic and molecular analysis.
With such a vast distribution covering North to South America, there are many variations in leaf shapes and sizes. Aquarists usually see two distinct varieties. The most available, narrow leaf variety exhibits dark-green leaves only 1 to 2 mm (1/16 inch) wide, reaching a height of up to 70 mm (3 inches). New leaves can achieve dark-red coloration given high light and good nutrition. The rarer broad-leaved variety has shorter, broader light-green leaves 4 to 5 mm (1/8 inch) wide at the base tapering to the tip, but it can grow as tall as 70 to 100 mm (3 to 4 inches). Even at high light intensities, this variety will not achieve any red color.
H. tenellum is undemanding and can be grown in medium to low light with no added fertilization or CO2. It can tolerate soft or hard water and can adapt to pH levels from 6.0 to 8.0 and GH values up to 20 degrees/350ppm.
H. tenellum is best used as a mid- to foreground plant. It is most always utilized as a lawn, since that is its natural growth pattern. In high-tech tanks, the narrow-leaved variety, due to the rich red coloration of the new growth, can quickly become the focal point to a layout. At other times, the use of sparse growth intertwined up through a smaller lawn of a different plant variety can add depth and dimension to the layout. It achieves a natural wild look that can be quite pleasing. More time and care is required to maintain such an appearance because the plant naturally wants to continue spreading and filling in. In an iwagumi layout, H. tenellum lends itself to being the second-tiered foreground plant.
Because it is naturally a plant of marshy habitats, H. tenellum is also well suited to paludariums and terrariums as long as the roots stay submerged. If grown emersed, the leaves will be wider and on shorter stems.
H. tenellum, whether grown emersed or submerged, spreads by runner chains (modified inflorescences) up to 50 cm (20 inches) in length, with plantlets forming every 2 to 5 cm (¾ to 2 inches). These plantlets can be detached and planted separately. In good light, with added CO2 and fertilization, a nice and thick rapidly expanding turf can be expected. Conversely, low light, with no added CO2 or extra fertilization, will result in slower, sparser growth. Once established, H. tenellum may require frequent pruning to keep it from invading the tank. It will also produce flowers when grown emersed, but runner production is less frequent.