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Re: Echinodorus tennellus
John Wheeler is having some difficulties finding a small form of E.
tennellus. Probably the best article I have seen to date on the Chain Swords
was written by Neil Frank and appeared in the Spring 2000 issue of Dave
Gomberg's Planted Aquaria Magazine. If you don't have the issue, maybe you
could order it as a back issue from Dave.
The hobby literature is full of errors in the names of the various small
sword plants and it can be beyond most hobbyists to figure out which is
which. The latest revision of Echinodorus was apparently done in 1994 and
lumps all new world chain swords into one of two species, E. tenellus
(narrow submerged leaves up to 0.4 cm wide) and E. bolivianus (submerged
leaves up to 1.0-1.5 cm wide). Neil points out in his article that there are
at least two varieties of E. tenellus in the hobby - one has tiny, 1 mm wide
leaves which are a dark green, becoming red under bright light, and the
other variety, which has leaves 4 mm wide and grass green in color. The
exact status of these two "races" isn't addressed by the revision of the
genus, although Neil made some attempt to backtrack them to older, now out
of date names. John is apprently looking for this "micro" variety but
finding that all of the commercial sources are selling the "normal" variety,
which can grow much larger.
The wider leafed chain sword, now apparently properly known as E.
bolivianus, exists in several forms as well and has in the past been
variously described and listed as E. angustifolius and/or E. quadricostatus.
Whether these variations are just normal variability within these two
species or whether they represent distinct subspecies or forms is way beyond
me - a lot depends on just what you mean by "species" and which "expert" you
believe. Some are much more "expert" than others - as has been shown on
numerous occassions, not all botanists are up to the task all of the time -
many of the determinations made be Rataj were later overturned by more
careful workers.
In my own tanks I have seen what I thought was the "micro" variety of E.
tenellus (well, it was "micro" for many years in one tank, and I acquired it
as such) suddenly explode when transplanted into another aquarium with
different growing conditions - the leaves are now longer and much wider than
they were previously.
A lot of the taxonomy problems might be done away with if and when DNA
analysis is done on a wider number of specimens and botanists can assertain
what the difference between normal variation within a species and
differences which could be considered genuine "species separators" (if they
can ever agree on the nature of a "species"). So far, ony 2 species of
Echinodorus show up in the NCBI Taxonomy Browser, so a lot of work remains
to be done.
Unless the experts state the basis for their species level (or even genus
level, in some cases) determination, it can be chancy to blindly follow the
names that are assigned to some plants. There has been such an explosion of
new information in the last 10 years caused by DNA analysis that many genera
of plants are going to need complete overhauls and that is going to take
some time (not to mention lots of money).
James Purchase
Toronto