The genus Echinodorus comprises 27 species found throughout
North, Central, and South America. The most recently described
species, Echinodorus floridanus (Haynes and Burkhalter), 1997,
is diagnosable from other North American Echinodorus species by
its large size, leaf shape, hardy rhizome, and stellate pubescence,
and is endemic to the Florida panhandle. We have hypothesized that
Echinodorus floridanus is closely related to South American
taxa based on shared morphological traits. From a cladistic analysis
of 127 morphological characters taken from 31 Echinodorus
species and subspecies we have hypothesized that E. floridanus
is closely related to South American taxa. Preliminary data using the
5S ribosomal DNA non-transcribed spacer (5S-NTS), a rapidly evolving
nuclear region also supports Echinodorus floridanus as being
sister to South American taxa, specifically to E. grandiflorus.
We discuss relationships within the genus, focusing on two major groupings,
and among putative outgroup taxa, providing characters uniting the various
groupings therein. The first grouping consists of
the 4 species of Echinodorus native to the United States while
the second group of interest, E. floridanus, E. grandiflorus, and
E. bracteatus, are of mixed geographic origin but appear to be
closely related to one another.
Key words: Alismataceae, Aquatic, Echinodorus, Endangered