# New Names for the pygmy chain sword plants



## Byron

Many planted tank aquarists are familiar with the *pygmy chain sword plants*. For many years they were deemed to be within the genus _Echinodorus_, and _E. tenellus_ has been the most widely available of the several very similar species. In 2007 the young Finnish botanist Samuli Lehtonen completed his doctorate on the subject of the natural history of _Echinodorus_, and several scientific studies have followed from him since then, with the result that the _Echinodorus_ genus has undergone a significant revision and the pygmy chain swords are now in the genus _Helanthium_. A number of aquarium plant nurseries are now using his revised names, along with the Royal Botanical Gardens at Kew and the International Plant Names Index. Dr. Lehtonen is a recognized authority on the Alismataceae; we are therefore following this classification henceforth in our plant profiles.

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_. With a few exceptions that grow fully submersed, the plants in these genera occur as amphibious bog plants, spending roughly half the year emersed during which time they flower, and the remainder submersed during the flooded period which lasts several months. Several of the species 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. 

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 elevated _Helanthium_ as a distinct genus and they assigned to it the dwarf chain sword species from _Echinodorus_. Pichon (1946) accepted this and further elevated _Albidella_ as a separate genus. In 1955, Fassett again considered the species within _Helanthium_ to be _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 this respect, though he increased the number of distinct species considerably.

In phylogenetic analyses (Lehtonen 2006; Lehtonen & Myllys 2008), _Echinodorus_ was found to be polyphyletic and in order to obtain a monophyletic circumscription of the genus, the classification proposed by Pichon (1946) was followed. _E. nymphaeifolius_ was transferred into the genus _Albidella_, and _E. bolivianus, E. tenellus and E. zombiensis_ were transferred into _Helanthium_. 

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. They are distributed from the temperate USA down to Argentina, and all species are amphibious bog plants. 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.

The number of actual pygmy chain sword species has long been a matter of debate. Haynes and Holm-Nielsen (1994) proposed two species, a narrow-leaf sword (_Echinodorus tenellus_) with a leaf width of 4mm or less, and a wide-leaf sword (_E. bolivianus_) with a leaf width of 1-1.5 cm; the remaining “species” were deemed variants of one of these. Christel Kasselmann subsequently noted that some of the wide-leaf forms have distinctive genetic makeup and advocated that the distinct species should be retained. Rataj (2004) listed nine species in his Tenellii group. The IPNI (following Lehtonen & Myllys 2008) currently lists five species, now under the genus _Helanthium,_ as follows:

_Helanthium bolivianum_
_Helanthium nymphaeifolium_
_Helanthium parvulum_
_Helanthium tenellum_
There are two 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. The species epithet is now _tenellum_ rather than _tenellus_ to agree with the gender of the genus name.
_Helanthium zombiense_

*References:*

Britton, N.L. (1905), _Alismaceae_, Manual of the Flora of the northern states and Canada, 2nd ed, Holt & Co., New York.

Costa, J.Y., E.R. Forni-Martins and A.L.L. Vanzela (2005), “Karyotype characterization of five Brazilian species of _Echinodorus_ (Alismataceae) with chromosomal banding and 45SrDNA FISH,” Plant Systematics and Evolution Vol. 257, Nos. 1-2.

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].

Kasselmann, Christel (2002), _Aquarium Plants_ [translated by Ulf Kotlenga].

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.

Pichon, M. (1946), “Sur les Alismatacees et les Butomacees,” Notul. Syst. (Paris), No. 12, pp. 170-183.

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.


*Addendum*

Cladistics is a method of systematic analysis for establishing and demonstrating phylogenetic relationships between taxa [the plural of taxon, which means a group or clade of organisms], and reflecting their origins.This method uses the following assumptions:

1. All species originate from other species, and are therefore related to other species in an ancestor-progeny relationship;
2. Species change their features over time, and those features are passed on to the progeny.

The phylogenetic analysis is based on establishing which features found in the group under study are relatively primitive and which are more recently derived, as well as on grouping taxa on the basis of derived features shared by all members of the group. A group (taxon) is termed monophyletic if it consists of the last common ancestor and all descendants; whereas polyphyletic means that the last common ancestor is not included in the group. When classifications are based on phylogenies we can ascertain and predict how that group of related fish function, and since this tells us something about their behaviours and requirements, it is of interest to aquarists.


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## JohnnyD44

once again, ridiculously awesome stuff, B!


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## Inga

Interesting! See, I really do learn something new every day. Thanks for sharing.


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## redchigh

interesting.


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## Byron

Dr. Lehtonen has significantly revised the entire genus, down to 28 valid phylogenetic species from the 52 in Rataj's 2004 revision of the genus. I have read Dr. Lehtonen's work which I have, and corrected our profile of Echinodorus major [was E. martii] as this species has been back and forth so much it is often under either or both names anyway, and E. major is undoubtedly correct. This one should cause little difficulty for aquarists.

The other species revisions are very significant. Our old familiar E. bleherae [E. bleheri was Rataj's incorrect original name, he corrected it], E. amazonicus and E. parviflorus are all gone (the names that is) as they are not valid species but variants of Echinodorus grisebachii which is a morphologically highly variable species to quote Dr. Lehtonen.

I am for the present waiting to see if Kew and the Internation Index follow Lehtonen before I tackle these three and others in our profiles.


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