Author's note (2008): Through a recent analysis of molecular markers and morphology, Samuli Lehtonen (Univ. Turku, Finland) concludes that the chain swords should be reclassified into the old genus Helanthium (See here). Now we wait to see if the scientific community accepts this revision. Samuli also notes that the original spelling of the genus name is Helanthium (=swamp-flower). The name was misspelled about 100 years ago as Helianthium (=sun-flower), and mostly the incorrect spelling has been used ever since. For example, see here.
There are several plants of the genus Echinodorus which can propagate by runners. These are commonly know as the chain sword plants. Like other plants of the genus, their emergent leaves are lanceolate or sword-like in appearance. Under proper conditions, these rosette plants can form dense lawns in the aquatic garden. Some of the smaller varieties are also an ideal foreground plant and an excellent ground cover. Over the years, the English language aquarium literature has used various common names for these plants such as "pygmy chain sword," "dwarf amazon sword" and "junior sword." The first time these plants can be found in the American aquarium literature is the August 1949 issue of William T. Innes' Magazine, The Aquarium (1). Albert Greenberg describes the "Pygmy Chain Swordplant" as a new plant collected in the Brazilian jungle by Mr. H. Greim of Rio de Janeiro. In the same issue, these plants were also advertised for sale in the U.S. thru Greenberg's Everglades Aquatic Nurseries of Tampa. The ad lists the new "Pygmy Chain Swordplant" as Echinodorus tenellus, growing from 2 to 4" and the wider leaf "Junior Amazon Swordplant" as an unidentified Echinodorus species which is said to be ideal for the smaller aquarium and grows from 6" to 8" in height. These particular specimens are probably the original breeding stock for today's commercial production by aquarium plant nurseries in the U.S. Now, these plants are commonly sold as "narrow leaf chain sword" and "wide leaf chain sword."
Greenberg's Pygmy Chain Sword, from THE AQUARIUM magazine, 1949 |
Greenberg's "Junior Sword," from THE AQUARIUM magazine, 1949 |
The first American book to show the Pygmy Chain Sword and Junior Amazon Swordplants was Exotic Aquarium Fishes, 12th edition (1951).(2) It shows the same pictures from The Aquarium magazine, but with transposed captions - the picture of the wide leaf chain sword is labeled the Pigmy Chain Swordplant, (Echinodorus tenellus) and the picture of the narrow leaf chain sword is described as a tall Vallisneria like variety with leaves about 10 inches in height. The latter plant picture with same caption and writeup also appeared in the 13th edition, but all subsequent editions thru the revised 19th edition published in 1966 only shows the wide leaf plant which is labeled E. tenellus . I do not believe this is a picture of E. tenellus.
Books published over the past several decades have used as many as a dozen different scientific names for the chain swords and have illustrated the specific plants with very different looking plants. Many of these names can be traced to various taxonomic revisions of the genus(3), (4) but the scientific names for these plants have not been used in a consistent manner in the American aquarium literature and were not always associated with proper pictures. In fact, the scientific literature recognized many different forms of the chain swords, each with different geographic coverage and physical characteristics. As early as 1940, it had been known that E. tenellus was indigenous to the Southern U.S.(5) In 1955, Fassett documented the distribution for this plant and its chaining relatives throughout North, Central and South America.3 All sword plants in the hobby, however, were generally reported to have originated from South America and described as perennial growers. The aquarium hobby literature often used its own names which propagated from publication to publication. In the 1955, Handbook of Tropical Aquarium Fishes,(6)Axelrod and Schultz, illustrate a plant called the Pygmy Chain Sword Plant as a wide leaf form which they called E. intermedius(7) and they also show two varieties of plants called E. tenellus. One illustration is for the 'junior sword plant' as shown by Innes and the other appears to be an small leaf variety of E. tenellus. In 1957, the more widely published Encyclopedia of Tropical Fishes(8)also illustrated a wide-leaf Pygmy Chain Sword called Echinodorus intermedius and another smaller variety called Sagittaria microfolia. Review of the aquarium literature of the 1960's and 1970's(9) (10), (11) reveal many other names for chain swords, including E. magdalenensis, E. grisbachii, E. subulatus, E. parvulus and varieties such as E. tenellus var. microphylla, E. tenellus var. parvulus, E. tenellus var. angustifolia, etc. As discussed below, these and other names have since been abandoned or associated with other plants. This lack of consistency with pictures and nomenclature, however, have caused a great deal of confusion for the typical aquarist who may wonder "What plant is the real pygmy chain sword?"
Aquarium books of the late 1970's thru the mid-1990's tried to follow the nomenclature established by Rataj. 5, (12), (13) He re-assigned the name E. tenellus to the smallest plants of the group and also called it the pygmy chain sword. He also classified other sword plants into E. latifolius, E. quadricostatus, E. angustifolius, E. austroamericanus, and E. isthmicus.(14) Rataj later noted that several species have more than one variety and that there may also be hybrids. He also mentions a chain sword species from Africa - E. humilis. Although his classifications were frequently questioned by the scientific community, at least he attempted to assign unique names to plants which had different geographic origins and physical appearance. He also notes that E. tenellus is a very variable species, according to the ecological conditions and according to the geographic area.14, (15)
The most recent revision to Echinodorus by Haynes and Holm-Nielsen(16) tries to simply the situation by lumping all of the new world chain swords into two separate species: a narrow leaf plant, E. tenellus, whose submersed leaves are described as generally up to 0.4 cm and the wider leaf E. bolivianus with leaves are 1-1.5 cm. Although this classification may be useful from a botanical point of view, it makes life much more difficult for aquarists. We know that there are at least 2 varieties or races of the plant now called tenellus (including one whose leaves are a tiny one mm in width). This is the variety which Rataj formally called E. tenellus var. tenellus and is possibly the plant illustrated in the early U.S. books as Sagittaria microfolia.8 While the broader variety of tenellus with 4 mm leaves is grass green, the leaves of the small variety is dark-green which becomes reddish in bright light. This has been widely noted in the aquarium literature but sometimes with the earlier name of Echinodorus tenellus var. tenellus (17), (18) and later with the current name of E. tenellus. (19), (20), (21) However, both size forms of E. tenellus are not reported in some aquarium books. Regarding the wide-leaf chain sword, E. bolivianus: there are several different forms as well. Kasselmann has pointed out that there are some of these wide-leaf chain swords cultivated in aquariums in Europe and the US which should retain their own unique names.(22) These include the tall Echinodorus angustifolius and wide leaf E. quadricostatus. While they may not always clearly look different than the other wide leaf chain swords, they do have different genetic makeup. Kasselmann notes that these triploid plants may be a result of a hybridization or of a mutation.
The sword plants including the chain swords are amphibious bog plants that typically spend some of their time underwater, and the remaining time with the leaves out of the water. Although botanical classifications are based on the emersed leaves as well as the seeds and flowers, the submersed leaves may be very different in appearance and quite variable. Such is the case with chain swords. Unfortunately, the descriptions in the aquarium literature are often based on the more commonly available information on the aerial leaves and published articles or books have not always pointed out the important differences between underwater and emergent growth. First, the stem is distinct and usually longer than the leaves. The stronger emergent leaves of all species are distinctively sword shaped, while the submersed leaves have different shapes (e.g. E. tenellus are more linear or grass-like). In addition, the submersed leaves of many sword plants species may not have a noticeable stem or petiole. Aquatic plant nurseries raise many if not most of the chain sword plants out of the water, (either as marsh plants or using hydroponic methods). So the plant you find in the aquarium shop in the small plastic pot filled with rock wool will have relatively stiff fleshy emersed leaves with long stalks which may be quite different than the pictures of submersed plants found in some of the better aquarium plant books. Moreover, without measurement data, the emergent varieties of chain swords can seem much closer in appearance than their submersed counterparts.
Pictures of chain swords grown hydroponically at the aquatic plant nursery. The flowers are shown.
E. tenellus, normal variety , slide 10 |
E. tenellus, micro leaf variety, slide 9 |
Underwater picture of E. tenellus, normal variety with emersed grown leaves (typically sold as "narrow leaf chain sword") slide #8 |
Underwater picture of E. tenellus, micro leaf variety with emersed grown leaves (slide #7) |
Underwater picture of a E. bolivianus with emersed grown leaves |
Slides 11-12: Plants grown in plastic pots must be prepared for the aquarium. The rock wool that is used in hydroponic culture should be removed. If there are multiple plants in one pot, they should be carefully separated. This will allow help the plants establish more quickly and avoid transfer of large quantities of nutrients contained in the rock wool. Tweezers can be helpful.
E. bolivianus is illustrated.
Nursery E. bolivianus removed from pot, slide 11 |
Rock wool removed prior to planting, slide 12 |
Another enormous factor contributing to the aquarist's difficulty in differentiating these plants is the potentially large variability in the appearance of underwater leaves from the clones of a particular specimen. Depending on their growing conditions, the size and shape of the underwater leaves can be quite different. In fact, individual underwater specimens cannot be distinguished from one another unless they are growing under comparable conditions. Mature offshoots from a single plant can even look different in the same aquarium. In particular, the appearance of the underwater plant can change with the amount of crowding, light intensity and light duration. A petiole (i.e. leaf stem) of the underwater plant may be more apparent with short day lighting and for some species, the leaves are also less long. The figure below illustrates different underwater forms for four chain swords: E. tenellus, normal variety; E. tenellus, micro-leaf variety; E. bolivianus and E. quadricostatus. The latter plant is the version of E. bolivianus that is typically sold as wide leaf chain sword and is the same plant which has historically been described as E. quadricostatus.
Emersed leaves of E. bolivianus and E. tenellus Emersed leaves of 3 chain swords: E. bolivianus (14cm x 5mm), and 2 varieties of E. tenellus,'micro' (9cm x 3mm) and 'normal' (6cm x 4mm). The leaves are lanceolate (sword-like) with petiole (stem).
E. tenellus, submersed normal variety There are at least 2 varieties of E. tenellus. These submersed leaves of the broader (normal) tenellus show the variability of clones of the same plant grown under different conditions. The leaves become larger with crowding and less illumination. The leaves are typically 4 mm wide. The ones shown here are 12 and 22 cm in length, but can grow larger than 30 cm.
E. tenellus, submersed micro leaf variety Here are leaves of the small or micro leaf variety of E. tenellus (1-2 mm in width). Like the other variety of tenellus, they become larger with crowding and less illumination. The larger leaf (12 cm) came from a plant grown in a 30 gallon aquarium with 20 watts of flourescent illumination. With 3 times more light, the leaves become smaller (3-4 cm), darker and reddish in color.
E. bolivianus, submersed The new classification for the wide leaf chain swords include all plants whose leaves are typically more than 1 cm in width. Here are two clones of the same plant sold as E. bolivianus. The small leaf (12 cm x 6mm) was grown with 12 hours of artificial light (160 watts in a 75 gallon, 300 L, aquarium). The larger leaf came from a plant with short day (winter) illumination.
E quadricostatus, submersed Three submersed leaves of wide leave chain swords. The right and middle leaves are clones of the same plant grown under different conditions. The small leaf is typical of wide leaf chain swords with 12-hours of illumination in the aquarium. The left and middle leaves illustrate short day (winter) illumination which produces a stem and larger leaf blade. Each plant was sold as and is probably E. quadricostatus, but the one on the left may be a different variety of E. bolivianus.
The 2 varieties of E. tenellus illustrate differences in their leaf forms which change according to the degree of crowding and light intensity. For both varieties, their leaves can become longer with dim light or crowded conditions. In my very heavily planted 70 gallon tank - illuminated 12 hours per day with two 4-foot 40 watt Triton tubes - I have produced submersed leaves of the broader 4 mm E. tenellus over 30 cm in length. In the same aquarium, offshoots of the same plant in the open, less crowded, better lit areas are only 10-12 cm. The latter is the typical size reported for this species.(23)
|
Caption for Slide 2c The submerged form of E. tenellus, both varieties, can be small and
large in the same tank. Crowded plants in the corners will be much taller than the ones in
the open areas.]
|
These tenellus have been growing in this aquarium for over 8 years, so I cannot rule out the possibility that they are now hybrids. This variety of "normal" tenellus is the one currently grown commercially in the U.S. and sold as the narrow leaf sword plant. I have also made similar observations with the small variety of tenellus. I obtained my "micro" leaf tenellus from a collector who obtained this plant in northern South America. This plant has extremely narrow leaves (only 1 - 2 mm in width) and grows 4 cm in bright light to 16 cm in dimmer and more crowded conditions. Although cultivation is not the focus of this article, I should mention that I have had good success growing both of these plants in a substrate that is composed of 50 percent peat moss and 50 percent coarse sand covered by a layer of coarse sand. This was widely recommended in some of the better plant books published during the 1960's. 9,10 Interestingly, these "soft-water" plants can be found in isolated wetlands called "Carolina Bays." These natural shallow depressions are scattered across the Eastern coastal plain, but found primarily in Georgia and the Carolinas. They are 30,000 to 100,000 years old or older, have a peat substrate and are largely fed by rain and groundwater.
|
[Caption for slide 3. Submersed micro leaf variety of E. tenellus. The leaves are 1-2 mm in width. With low illumination, their length can exceed 12 cm.] |
The submersed leaves for some species of Echinodorus change with the duration of lighting. The illustrated leaves for E. bolivianus and E. quadricostatus show these effects of photo period. For each species the short leaf is sessile (without stem) and is the result of a 12-hour photo period. The larger leaf has a distinct stem for both species, but their leaf shapes are clearly different. In both cases these larger leaves represent plants grown strictly under natural daylight during the winter with an 8-9 hour illumination period.
|
Slide 4b. Submersed E. quadricostatus grown under short-day illumination. Note the long stem and completely different leaf shape |
|
Slide 5b. Submersed E. bolivianus grown under short-day illumination. Note the long stem and different leaf shape |
My size data for the Echinodorus tenellus, (sold as the narrow leaf sword plant in the U.S.) match the description of the plant collected by Greim in the late 1940's, first described as E. tenellus and later portrayed in Innes' book as a tall "grass-like" plant. It appears that it may have been the "normal" variety of E. tenellus which can grow tall under certain conditions.
I also believe that Greim's plant which was illustrated as the Junior Sword Plant and later as the Pygmy Chain Sword is a probably a variety of E. bolivianus and may possibly be E. quadricostatus. In any event, it could be the source material for the plant which is currently sold as the wide leaf chain sword.
These observations highlight the extreme variability of these plants and the difficulty in making
generalizations from a limited range of aquarium conditions. Don't be surprised if your tenellus
never gets taller than 5-10 cm (2-4 inches) or if it grows right up to the top of an 18 inch, 75
gallon (300 L) tank.
|
Eleocharis baldwinii(also called Eleocharis parvulus), sold as "Hair Grass". This grass like plant has very fine leaves. It is native to the southern U.S. and is found in similar soft water environments as E. tenellus. An emersed grown plant with flowers is shown. When these potted plants are available in aquarium shops, the top part of the leaf with the flowers has been cut off. |
|
Lilaeopsis carolinensis. This plant has recently become available in the hobby. It can be found in the Carolinas and elsewhere in the Southeastern US. It's leaves are taller and thinner than L. brasiliensis and does well in soft water. A nursery grown plant with its emersed leaves is shown. |
|
Lilaeopsis brasiliensis ( incorrectly called L. novae zelandiae), sold as "Micro Sword" and can be found in individual pots or large mats. This grass like creeping plant originates from Brazil. There is actually a different plant called L. novae zelandiae which is native to New Zealand. Lilaeopsis brasiliensis is a light green plant with thin lanceolate blades 3-10 cm in length, 3 - 5 mm wide. As such, the leaf size and color is similar to that of E. tenellus. Unlike the chain swords, however, the leaves of Lilaeopsis do not grow in a rosette but instead grow from a creeping shoot. This plant will adapt to submersed conditions, but requires much more light than the chain swords in order for it to flourish. A nursery grown plant with its emersed leaves is shown. |
1. Greenberg Albert "The Family Echinodorus," The Aquarium, Vol. XVIII No. 8, Innes Publishing Co. Philadelphia PA., August 1949
2. Innes, Wm. T. Exotic Aquarium Fishes. Innes Publ. Co. 12th ed. 1951.
3. Fasset, N.C. Echinodorus in the American Tropics, Rhodora Vol 57. No. 677. May 1955
4. Rataj, Karel. Revision to the Genus Echinodorus Rich. CSAV. 1975.
5. Fasset, N.C. A Manual of Aquatic Plants. McGraw-Hill Book Co. 1940.
6. Axelrod & Schultz. Handbook of Tropical Aquarium Fishes. 1955.
7. E. intermediatus was also used to describe the "original" Amazon Sword Plant in the 1940's. This plant is now called E. grisebachii, and was formerly known as E. amazonicus and E.brevipedicellatus.
8. Axelrod & Vorderwinkler. Encyclopedia of Tropical Fish. T.F. H. Publications, Inc. 1957.
9. Roe, Colin D. A Manual of Aquarium Plants. Shirley Aquatics Ltd. 1967.
10. Stodola, Jiri. Encyclopedia of Water Plants. T.F.H. Publications, Inc. 1967.
11. Wit, H.C.D. de. Aquarium Plants. Blandford Press, English Edition, 1964
12. Rataj, Karel and Thomas J. Horeman. Aquarium Plants. T.F.H. Publications, Inc. 1977.
13. Mühlberg, Helmut. The Complete Guide to Water Plants. EP Publishing Limited. 1982.
14. The complete names for the six species of Echinodorus and their varieties which reproduce by runners as described by Rataj are:
Echinodorus tenellus (MART.) BUCH.
Echinodorus tenellus var. tenellus
Echinodorus tenellus var. parvulus (ENGELM.) FASSETT
Echinodorus latifolius (SEUBERT) RATAJ
Echinodorus quadricostatus FASSETT
Echinodorus quadricostatus var. xinguensis
Echinodorus angustifolius RATAJ
Echinodorus austroamericanus RATAJ
15. Rataj, Karel Alismataceae of Brazil, Acta Amazonica, Supplement 1 Vol. VIII No. 1 March 1978.
16. Haynes, Robert R. & Lauritz B. Holm-Nielsen: The Alismataceae, Flora Neotropica 64:1-112. The New York Botanical Garden. Source: Organization for Flora Neotropica, The New York Botanical Garden, Bronx, NY. 1994.
17. Scheurmann, Ines. Water Plants in the Aquarium. Barron's. 1987.
18. Riehl, R, and H.A. Baensch. Aquarium Atlas. Tetra Press. 1987.
19. Riehl, R, and H.A. Baensch. Aquarium Atlas, Volume 3. Tetra Press. 1996.
20. Dennerle, Ludwig and Hans Lilge. System for a Problem-Free Aquarium. Warda-Druck. 1993
21. Horst, Kaspar. My First Aquarium. Aqua Documenta. 1993.
22. Kasselmann, Christel. "Book review: The Alismataceae." The Aquatic Gardener, Vol 11 No. 5, September-October 1998.
23. James, Barry. Aquarium Plants. Salamander Books Ltd. 1986. The British author James describes the 'standard' commercially available variety as reaching 6 inches (15 cm), but notes that there are several races and growing forms with both smaller and larger varieties.
[Author's Note: Add the following Reference if Lilaeopsis pictures are used.]
24. Affolter, James. A Monograph of the Genus Lilaeopsis (Umbelliferae). Systematic Botany Monographs, Volume 6. The American Society of Plant Taxonomists. 1985.
|
This page was last updated Thursday, November 27 2008
|
|
