Scientific Name: Echinodorus Tenellus (Helanthium Tenellum)
Common name: Mini Amazon Sword, Pygmy Chain Sword
Height: under 10 cm (3.94 inch)
Lightning: 0,70 wats/litre
Temperature: 18 °C – 28 °C
pH tolerance: 6,5 – 7,2
Water hardness tolerance: 5 – 12 °dKH
Special requirements: CO2,
Utilization of the plant: aquarium
Location of the plant: forefront
This is a classic among all available foreground plants. It has been around for a long time. This ‘Tennellus’ is the narrow-leaved form – which has a slightly darker colouration than the light green form. However, its temperature max of 28°C makes it an ideal plant for Discus tanks. The plant grows into a dense carpet.
Shortly after planting, all the substrate is covered. Despite its dense growth, it does not tend to compete for space as Glossostigma elatinoides does with several layers forming over time. This makes it an ideal, low-maintenance plant. Long blades can be easily trimmed.
Two quite distinct varieties are known in the aquarium trade. The most commonly sold form has narrow dark green leaves only 1-2 mm wide. The most recently formed leaves can have a dark red coloration under good lighting and nutrition. A much less common variety has light green leaves that are much shorter and broader, being up to 4 mm wide at the base, tapering from the base to the tip. In the broad-leaved variety, there is no tendency to produce red pigmentation. Plants of the second variety, if uncrowded, stay very low to the substrate, whereas the first variety produces upright leaves, even if uncrowded.*
H. tenellum spreads rapidly by runners, forming a dense turf in good light and a much more sparse growth in shaded areas. While growth is faster with CO2 fertilization, the plant grows well in tanks where the fish provide the only CO2. Frequent pruning is necessary to keep it from invading every part of the tank. Emersed, the narrow leaved variety produces a very delicate, small plant with tiny flowers, whereas the broad leaved variety produces a considerably larger, more robust plant.
This plant has long been known under the name Echinodorus tenellus and will likely still appear as such for some time; the explanation for the recent reclassification is given below. The species epithet tenellus is changed to tenellum to agree in gender with the genus name Helanthium.
As with all species in this genus, Helanthium tenellum can be grown permanently submersed or emersed as a bog plant in paludariums and terrariums provided the roots are permanently submerged. When grown emersed, the leaves are oval and on short stems, and flowers will be produced. If planted in the aquarium, the new leaves will be awl-shaped phyllodes (stemless linear and narrow leaves), and the emersed leaves will yellow and die off. Submersed phyllodes (leaves) are variable and there are two generally-recognized variants: the “narrow leaf” has a leaf width of 2mm (1/16 inch) and grows to 3 inches or sometimes a bit taller; under bright light the leaves may turn slightly reddish. The “wide leaf” has a leaf width of 5mm (1/8 inch) and attains 3-4 inches in length but in lower light it may grow to 10 inches.
In both the emersed and submersed forms, it reproduces vegetatively by sending out numerous runners on top of the substrate from which plantlets will emerge every couple of inches and root in the substrate. It spreads rapidly once it is settled into the aquarium, and may be controlled by cutting off the runners as needed; the daughter plants can be re-planted. The lighter green leaves contrast nicely with other plants including the larger swords that are a darker green.
Given the large distribution of this species, it is not surprising that there are several variations, differing in the size of the leaves and the shape of the achenes which are the dried fruits containing one seed (Rataj & Horeman, 1977). Nurseries frequently supply Echinodorus bolivianus as E. tenellus but the two species are easily distinguishable; E. bolivianus has three rows of chlorophyll-free pullucid “windows” adjacent to the leaf spine, while E. tenellus has normal (green) tissue throughout the leaf (Rataj, 2004).
This species was originally described by Buchenau in 1869 and placed in the genus Echinodorus, the second-largest genus of aquatic plants in the Alismataceae family.
The Alismataceae is a family of aquatic herbs containing 12 genera with about 80 species that are distributed in the tropical and subtropical regions of both hemispheres. Three genera of interest to aquarists occur in the Neotropics [=tropical regions in the Americas]: Sagittaria, Echinodorus and Helanthium. The species in these genera are quite similar in appearance, making it difficult for aquarists to differentiate between them. To add to the confusion, even within each species the plants can take on quite different leaf lengths depending upon the conditions in the aquarium. With a few exceptions that grow fully submersed, the plants are amphibious bog plants in their habitat, spending roughly half the year emersed when they flower, and half submersed during the flooded period which lasts several months.
The group Helanthium [the spelling Helianthium with the first "i" is incorrect] was described by Engelmann, Bentham and Hooker in 1883 as a section in the genus Alisma. In 1905, Engelmann and Britton erected Helanthium as a distinct genus and they assigned to it the dwarf chain sword species from Echinodorus. In 1955, Fassett reversed this and considered the species within Helanthium as Echinodorus; however, he divided the genus into two subgenera, Helanthium and Echinodorus. Helanthium held two sections, Nymphaeifolii (containing one species, Echinodorus nymphaeifolius) and Tenellii that contained the several closely-related species with E. tenellus as the type species. The subgenus Echinodorus held nine sections containing the remaining species within this genus. In his recent revision of the genus Echinodorus, Rataj (2004) followed Fassett (1955).
In phylogenetic analysis (Lehtonen 2006; Lehtonen & Myllys 2008) Echinodorus was found to be polyphyletic [=the last common ancestor is not included in the genus] and in order to obtain a monophyletic [=a clade (here genus) consisting of the last common ancestor and all descendant species] circumscription of the genus, the classification proposed by Pichon (1946) was followed by Lehtonen. E. nymphaeifolius was transferred into the genus Albidella, and E. bolivianus, E. tenellus and E. zombiensis was transferred into Helanthium. A number of prominent botanists and institutions including several suppliers of aquarium plants are now accepting this reclassification, including the Royal Botanical Gardens at Kew (a major authority among botanists) and the International Plant Names Index. We are therefore following this classification.
The species now in Helanthium are those former Echinodorus species that have traditionally been considered within the generic common designation of dwarf chain sword plants and are smaller than the true Echinodorus species, though leaf length can vary greatly depending upon conditions in the aquarium. The same species grown in two aquaria can look different, and within the same aquarium two plants of the same species may appear slightly different. The number of species varies according to author, from 5 (Lehtonen) to 9 (Rataj). They are distributed from the temperate USA down to Argentina, and all species are amphibious bog plants that grow emersed and submersed. Regardless of whether they are cultivated emersed or submersed, these species propagate vegetatively via runners up to 50 cm in length from which plantlets arise at intervals of 2-5 cm. They also produce inflorescences when growing emersed which produce flowers but adventitious plants are rare.