Ok, we're heading for the deeper waters.
The runner producing swords, or grass-like ones, make what is called 'pseudostolons'. They are not real stolons (runners) apparently but a modification of the flower stalk. Their modified flower stalk can keep growing apparently ad infinitum
and making more plantlets. The flower stalks of the Echinodorus sensu stricto
can't keep on growing like this. Furthermore, there are many other morphological characters that separate these two, and Lehtonen (& Myllys) has not been the first to define these runner-making swords as a genus of their own. However, the study of Lehtonen shows that this group of plants is different from the Echinodorus
also genetically (and is quite far removed from them actually).
The above mentioned article came out this year (see the link in the first post). So it's very official. The article has gone through referees and the magazine is one of the most respected ones in the field of the cladistics. You are right in the sense that there is no one body for classification but the community of the researchers. The earlier classifications of the genus Echinodorus
have no more (but maybe less?) validity to the Lehtonen's.
Let's take some examples:
The most widely distributed revision (in aquarium circles) of the Echinodorus
is that of Karel Rataj's (1975). Most of the sword names still in use are from it. However, it is unreliable as many botanists have shown and heavily critisized. Rataj is/was not even a biologist. In 1975, he accepted 6 species of runner-making swords with 5 different variaties. One of these was E. quadricostatus
(the type species of which is from South America and not from Cuba, btw.).
In 1994, Haynes & Holm-Nielsen, two botanists, revised the genus. In their scientific classification, there are only 2 species of runner-making swords: E. tenellus
& E. bolivianus
. One of the synonyms under the E. tenellus
is Echinodorus parvulus
described by Engelmann in 1856. This is the only native runner-making sword in the States. (Yes, there is an Eleocharis parvula
, too. Nothing to do with ex-Echinodorus parvulus
Lehtonen's new revision of the genus should come out this hear. It has already been accepted for publication in the Kew Bulletin (the
magazine of the botanists). It will include 2 new Echinodorus
species but won't treat Helanthiums
as are they are not anymore in the same genus.
Sorry for the long post.