Tropical Fish

Tropical Fish Keeping - Aquarium fish care and resources » Tropical Fish Profiles » Chain Sword

Chain Sword

Scientific Name: Helanthium bolivianum
Family: Alismataceae

About the Chain Sword

Species Type: Freshwater Plants
Category: Substrate Rooted

Care Level: Very Easy. Adaptable, will tolerate soft or hard water, low light, very minimal or no additional fertilization. pH 6.0 to 8.0 and GH up to 20 degrees/350ppm.

Origin: Neotropical; reported from areas in Mexico, Central America, West Indies, and South America down to northern Argentina.

Physical Description

This plant is frequently confused with the similar pygmy chain sword, Helanthium tenellum [see that profile]. Nurseries frequently supply H. bolivianum as H. tenellum but the two species are easily distinguishable; H. bolivianum has three rows of chlorophyll-free pullucid "windows" adjacent to the leaf spine, while H. tenellum has normal (green) tissue throughout the leaf (Rataj, 2004). The subject plant is also larger in leaf length and width.

A recent variant with twisted leaves resembling a corkscrew Vallisneria originated as a natural mutation in a Singapore nursery. This form is commonly called Vesuvius Sword, named for the spiraling shape of the leaves that resemble the smoke that came from Mount Vesuvius when it erupted. Scientifically, this form is Helanthium bolivianum "Vesuvius."

The various chain swords have long been classified in the genus Echinodorus, and Rataj (2004) lists nine species; the explanation for the recent reclassification is given below. The subject species was Echinodorus bolivianus, and the species epithet is changed to bolivianum to agree in gender with the genus name Helanthium. Plants under names like E. quadricostatus are now deemed to be the subject species.

As with all species in this genus, Helanthium bolivianum 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 but normally have a leaf width of up to 1.5 cm (5/8 inch) and can attain 15-20 cm (8 inches) in length depending upon light intensity.

In both the emersed and submersed forms, it reproduces vegetatively by sending out numerous pseudo-stolons on top of the substrate from which plantlets will emerge every couple of inches and root in the substrate. These pseudo-stolons are usually referred to simply as "runners" but technically they are not true runners (stolons) but a modification of the flower stalk. 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.

This species was originally described by Rusby in 1947 in the genus Alisma; the species epithet is Latin and means originating from Bolivia. In 1979, Holm-Nielsen moved it into Echinodorus, the second-largest genus of aquatic plants in the Alismataceae family [see further taxon data below].

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 were 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 chain sword plants (because they reproduce in aquaria via "runners") 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.

Aquarists who propagate aquarium plants have always recognized that while the various species in Echinodorus will readily hybridize, some even naturally--producing the many new red, spotted, and marble leaf forms--the chain swords have resisted hybridization with species in Echinodorus; this lends credence to the view that the two genera are distinct.

References:

Fassett, Norman C. (1955), "Echinodorus in the American Tropics," Rhodora, Vol. 57, No. 677 (May 1955).

Frank, Neil (2000), "The Chain Sword Plants: History and Nomenclatural Perspectives," Aquatic Gardeners Association [online].

Lehtonen, Samuli (2007), "An integrative approach to species delimitation in Echinodorus (Alismataceae) and the description of two new species," Kew Bulletin Vol. 63, No. 4, pp. 525-563.

Lehtonen, Samuli and Leena Myllys (2008), "Cladistic analysis of Echinodorus (Alismataceae): simultaneous analysis of molecular and morphological data," Cladistics, Vol. 24, No. 2 (April 2008), pp. 218-239.

Rataj, Karel (2004), "A New Revision of the Swordplant Genus Echinodorus Richard 1848 (Alismataceae)," Aqua--Journal of Ichthyology and Aquatic Biology, Special Publication No. 1, March 2004.

Ideal position in aquarium

A fore-ground and mid-ground plant in large tanks, or background in smaller tanks.

Lighting requirements

Low to moderate; under brighter light the leaves will be smaller [see additional comments under Physical Description].

Growth rate

Medium

Minimum Tank Suggestion

N/A

Ideal water parameters for Chain Sword

Soft to moderately hard (4 to 15 dGH), acidic to basic (pH up to 7.5), temperature 22-30C/72-86F.


All times are GMT -5. The time now is 08:29 PM.