DNA fingerprinting of Hydrilla, Egeria, and Elodea (Hydrocharitacea) reveals new information on their range and recent history

Background/Question/Methods DNA fingerprints provide a means to positively identify plant species from tiny fragments of fresh or dry plant tissue and provide quality assurance for determining plant distribution.  We questioned if a simple species level taxonomic fingerprinting techniques could be developed for submerged aquatic vegetation (SAV) and used to reduce errors in identification.  We tested the hypothesis that the use of fingerprinting would substantially improve current and past descriptions of SAV.  We focused our fingerprinting efforts on four related and similar appearing species that rely on vegetative propagation, reproduce via fragmentation, and all have non-dissected leaves occurring in whorls.  We developed a fingerprinting protocol based on a polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis to discriminate among four morphologically similar SAV species, the North American invasive species, Hydrilla verticillata (monoecious and dioecious) and Egeria densa, and the European invasive species, Elodea canadensis, and Elodea nuttallii.

Results/Conclusions We verified the technique on ~ 100 herbarium and live samples and found fresh tissue or freshly frozen tissue more reliably yielded usable products.  Confirming and correcting historic identifications that were based only on morphology, yielded surprising findings that affect understanding of distribution and range, timing of introductions, and rate of spread of these species.  Misidentifications were most likely with Hydrilla and Elodea and least likely with Egeria densa.  We found a large percentage of the putative E. canadensis samples from the USA were in fact E. nuttallii.  The development of these fingerprinting tools will be helpful for any validation study of the range of E. canadensis with E. nuttallii.  We also confirmed new locations where the monoecious and dioecious H. verticillata biotypes had recently increased their range to the north in the USA.  This study shows that once protocols are developed, molecular techniques provide an accurate method for confirming identification, distribution, and recent pace of spread of invasive and non-invasive species.