Origin and Habitat: This species has an extensive range, including the SE United States, Caribbean islands, parts of Mexico, northern coastal areas of Columbia and Venezuela, and the Pantanal area in Brazil and Paraguay. It is found in boggy locations.
Ideal position in aquarium
Background or specimen plant for the larger aquarium.
Moderate; brighter light and longer duration will result in emersed leaf growth [see above under Physical Description].
Minimum Tank Suggestion
Soft to moderately hard (hardness to 15 dGH), acidic to slightly basic (pH to 7.5) water, temperature 20-28C/67-83F.
One of the largest of the Echinodorus for aquaria, this species makes a superb specimen in tanks 3-4 feet in length and is excellent as a corner or background plant. In open-top aquaria leaves will often grow emersed (above the surface). The size is dependent upon the light and nutrient availability; brighter light or a light period of 12+ hours will result in larger leaves above the surface; less light (11 hours duration) will restrain growth, and removing large older leaves and occasionally trimming the roots will keep the plant from growing too large.
The petiole [leaf stem] is triangular, with ovate to oval blades growing 7-30 cm in length and 4-20 cm in width. Blades are usually acute [pointed tip] with 5-9 longitudinal veins and are light to medium green, sometimes displaying reddish spots; new leaves regularly appear from the centre of the crown and the initially-brownish blades unfold and become light green as they grow somewhat slowly towards the surface.
Adaptable to basic (alkaline) water, it nonetheless tends to grow better in slightly acidic water. A very extensive root system develops, spreading out for several inches. Inflorescences (floral stocks) will produce adventitious plants when the parent plant is growing submersed; after a few weeks, these can be carefully removed from the stalk and planted as new plants, or left on the inflorescence.
Originally described by Grisebach in 1857; the species epithet refers to the cordate leaves. Several authors have considered this plant to be E. ovalis or E. fluitans; Haynes & Holm-Nielsen (1994) proposed that the three were a single polymorphic species having the subspecies E. cordifolius cordifolius and E. c. fluitans. Lehtonen's (2007) phylogenetic analysis established E. fluitans as conspecific with E. cordifolius, and E. ovalis is not a distinct species but is within the E. cordifolius-ovalis clade. Engelmann (1848) named this plant E. radicans, which was based on the type for Sagittaria radicans described by Nuttall (1835); this sword plant may still be encountered under the common name of radicans sword.
Some of the most beautiful and useful plants for the tropical aquarium are found among the Echinodorus, a genus distributed in the tropical and sub-tropical regions of the Americas from the lower United States down to Argentina; the two "African" species of Rataj are almost certainly erroneous (Kasselmann, 2003). The genus name derives from the Greek echinos [hedgehog] and doros [pipe or hose] referring to the spiny fruit. The English common name "sword plant" comes from the general lanceolate shape of the leaf of most species and is generally used for all plants in this genus although other non-Echinodorus plants may sometimes appear under the name "sword."
Larger-sized species have a rhizome, whereas smaller species are stoloniferous. All species are perennial or annual aquatic or marsh plants found in boggy flood areas or along the banks of stagnant or slow-flowing waters. Except for the very few species that are permanently submersed, Echinodorus plants spend half the year emersed (when they flower) and the remainder submersed during the flood season. Leaves arise in a rosette and can be very variable not only between emersed and submersed forms but also when cultivated under different conditions. Correct identification often requires study of the flower. Inflorescences (flower stalks) are formed in all species; when grown permanently submersed in the aquarium most species will not flower but plantlets (daughter plants) will develop from the nodes on the inflorescence.
Confusion exists over the number of species, and many have been known under different names. In his earlier revision of the genus, Rataj (1975) listed 47 species. A major revision by the botanists R.R. Haynes and L.B. Holm-Nielsen (1994) lists 26 species. In 2004, Rataj increased the number of species to 62. More recent work by Samuli Lehtonen--incorporating cladistic analysis using morphological data--has proposed 28 valid species (Lehtonen, 2007).
Haynes, R.R. and L.B. Holm-Nielsen (1994), "The Alismataceae," Flora Neotropica, Vol. 64, pp. 1-112.
Kasselmann, Christel (2002), Aquarium Plants [English translation by Ulf Kotlenga].
Lehtonen, Samuli (2006), "Phylogenetics of Echinodorus (Alismataceae) based on morphological data," Botanical Journal of the Linnean Society, 150, pp. 291-305.
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.
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