In my ongoing research into the sword plants, I came across a paper that I thought some of you might find interesting.
Ther authors are Samuli Lehtonen and Daniel Falck, two Finnish botanists. Dr. Lehtonen is perhaps the most knowledgeable botanist when it comes to the swordplant species in the Echinodorus and Helanthium genera which he and his colleagues have significantly revised through the use of DNA sequencing and cladistic analysis.
This is the first scientific study of the many cultivars--the "Kleiner Bar," "Oriental," "Rose" and similar hybrid species. Those who often ask about the origins of these variants should find this interesting. But aside from the very scientific and technical portions, the authors provide a very good summary of the development of aquaria over the past 150 years, and planted aquaria up to the present.