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Family: Alismataceae

Common Name: Melon Sword

Origin: South America: southern Brazil

Ideal position in aquarium

An ideal specimen plant in any sized aquarium, though it may get a bit large for tanks under 20 gallons.

Lighting requirements

Moderate to bright. Leaf colour can be affected by the light intensity [see under Description].

Growth rate


Minimum Tank Suggestion

20 gallon

Water parameters for Melon Sword

Soft to moderately hard (hardness under 15 dGH) acidic to slightly basic (pH to 7.5) water, temperature 22-28C/72-82F. Well suited to harder water provided sufficient light and nutrients are provided.


One of the most beautiful of aquarium plants. Leaves up to 16 inches/40 cm grow from the robust rhizome, though in the aquarium leaves are usually much shorter and vary according to the light and nutrients. Young leaves are reddish-brown, turning bright green as they mature; in cooler aquaria and with brighter lighting the reddish-brown colour remains in mature leaves. The plant has moderate but distinctly undulate leaf margins, and the three to five longitudinal veins are very pronounced with distinct but less-pronounced cross veins.

Pale leaves indicate a lack of nutrients, and fertilizer should be given regularly. As with all Echinodorus species, this plant is a heavy feeder. Propagated in the aquarium by rhizome division but more commonly by adventitious plants arising around the mother plant or on the inflorescence.

As with the majority of species in this genus, E. osiris is a bog (marsh) plant in nature, spending half the year emersed (during which it flowers) and half submersed. It adapts well to fully-submersed conditions, although aquatic leaves will be quite different from emersed leaves, in shape, size and texture. Newly-purchased plants have often been propagated emersed by nurseries and have oval reddish-brown leaves; when grown in the aquarium the developing submersed leaves will be long and lanceolate, and the older leaves will yellow and should then be removed. In one of the photos below, the plant has both emersed and submersed leaf forms; as the plant adjusts to submersed growth, the emersed-form leaves will yellow and die and all new leaves will emerge from the crown in the submersed forum. The other photo shows subersed leaf forms only.

The species was described by Karl Rataj in 1970; the species epithet refers to the Brazilian aquatic plant nursery Lotus Osiris. The sometimes-encountered common name of "Red Amazon Sword" comes from the reddish-brown colouration of young leaves, and the common name "Melon" from the oval shape of emersed leaf form as can be seen in one of the photos below.

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 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 & Holm-Nielsen (1994) consider E. osiris as a synonym for E. uruguayensis. Kasselmann (2002) suggests it may be a natural hybrid and thus a distinct species. Four Echinodorus species--E. osiris, E. uruguayensis, E. opacus and E. grisebachii--have been observed growing together in southern Brazil, supporting this contention. Lehtonen (2007) also proposes E. osiris as synonymous with E. uruguayensis, and if this is accepted we should be prepared for significant re-naming within the genus. As the name E. osiris is so well known, we are retaining it for the present to avoid confusion.


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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