Echinodorus: Sword Plants

The genus Echinodorus, the Sword Plants from South America, are among the most used aquarium plants and some are among the easiest to care for. Most will outgrow a 10-gallon tank. Not all are from the Amazon basin, though it's the center of their diversity; some grow far to the north in Mexico and just over the border into US territory, while Echinodorus uruguayensis  is from Uruguay, naturally. Most are marsh plants by nature, and some make themselves unhandy in the aquarium by insisting on throwing up floating or aerial leaves: very nice in an open-top tank, where you can really enjoy the long flowering shoots with flowers at the nodes, which they'll stretch above the water surface, instead of pressing them below the water surface, as I have to do. Underwater the flowers don't open, but the shoots produce adventitious plants at the flowering nodes: when they've grown a good set of  roots, you can gently twist them free and plant them right up front for a while, until they get too big.
 
Many of the best echinodorus for aquariums are hybrids. Echinodous leaves are variable: the submerse leaves are soft in texture and more translucent, perhaps tending to olive-green or even reddish when they're new. The emerse leaves are leathery and opaque, suited for their dry environment. The two kinds of leaves may differ so much in shape that species have been unnecessarily multiplied by unwary botanists, to accommodate each variation. Conversely, Christel Kasselmann notices in her Aquarium Plants, dried herbarium specimens and details of flower and seed may unify as one species plant populations that differ a great deal when they're being grown in aquaria. Since she wrote, the taxonomy of Echinodorus has been revised and argued over in the first decade of the 21st century, the discussion now based on DNA rather than the variable and misleading morphology, giving some 28 natural species.
 
Echinodorus that you may see being grown in discus aquariums are getting by at the very top of their range of temperature tolerance, at 86^o; at about 88^o leaves and even crowns may seem to have melted irretrievably: if you refrain from handling the plant, the rosette may regenerate.