Cryptocoryne species

Cryptocoryne species. Several species of Cryptocoryne have been standard plants for the aquarium for the best part of a century, without ever developing a "common name": Crypts is as lame as it sounds. The pronunciation is CRIP-to-COR-inee. About a dozen species are generally available with some searching, of which only C. beckettii, C. wendtii and C. x willisii (actually an aquarium hybrid) are widely available at your LFS.  The olive-green leaves with garnet brown undersides of C. beckettii and C. wendtii offer contrasts with the greens of other aquarium plants.
 
 
Cryptocorynes are plastic species, in the sense that they are physically changeable according to the strength of light they receive, their pH, the substrate, and whether they are grown submerged or with emerse leaves, the only condition, generally speaking, in which they'll flower and can be identified as to species. One result is that researchers have needlessly multiplied the species, which are nowadays deflated in number once more and better distinguished than they used to be, using chromosome counts and the structure of their flowering. Ordinarily that only occurs when some of the leaves are growing emerse, above the water surface.  Their inflorescence is in typical aroid fashion, like Jack-in-the-pulpit or your Anthurium houseplant, presenting a spadix standing inside a narrow hooded spathe that may be extended to a long curling and twisting point, in colors that may mix white, green and bronzy purple.  The smell, if you get close, is often distinctly funky: most aroids are pollinated by flies.
 
Cryptocorynes will do best for you if your water is soft and your pH hovers below 7.  They form runners, sprouting daughter plants at intervals, so a few purchased plants can multiply into a stand of Cryptocoryne. They also resent being moved, so you need steely confidence sometimes when your nice stand "melts", its leaves collapsing into mush as a response  to abrupt change, whether it's been  a big water change recently, a few days of unaccustomed chill or heat, even a change in the light regime. Be patient: each growing point will quickly sprout new leaves.
 
Links. The North American Cryptocoryne Society maintains a forum at Aquatic Gardeners Association. Aqualand posts an article on Cryptocorynes with close-up illustrations.
 
Jan Bastmeijer's Cryptocoryne pages. Cryptocoryne genus at Wikipedia.