Heres one too
Scientific name: Echinodorus quadricostatus
Yes, this is actually
Helanthium bolivianum though one may still see it under the synonym
E. quadricostatus. As you brought this up, I can provide some explanation, as it gives me a chance to deal with taxonomy which is a passion of mine.
The various chain swords have long been classified in the genus
Echinodorus, and Rataj (2004) lists nine species as such; the explanation for the recent reclassification is given below. The subject species
Helanthium bolivianum 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 [more below on this too].
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.
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 further credence to the view that the two genera are distinct.
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 3 (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.
Turning now to "E. quadricostatus." Lehtonen & Myllys (2008) proposed three species for Helanthium, based upon their phylogenetic study of the plants' DNA, with the other "species" deemed synonymous to one of these three. These are listed in The Plant List under the three accepted species,
H. tenellum, H. bolivianum and
H. zombiensis. There are 15 "species" now accepted as
H. bolivianum. This is the direct link to that page:
Here are the references for the above:
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.
