The noncoding trnH-psbA spacer, as an effective DNA barcode for aquatic freshwater plants, reveals prohibited invasive species in aquarium trade in South Africa

• The identification of aquatic alien plants can be problematic even for experts.
• DNA barcoding has been efficient in assisting traditional identification methods.
• trnH-psbA is a reliable DNA barcode for invasive freshwater plants of South Africa.
• It also reveals that prohibited plants are traded in South Africa's aquarium market.
• We call for strict measures and environmental education of aquarium traders.

The negative effects of invasive alien aquatic plants raise concern globally. These effects are predicted to increase in the future due to a rapid development in transport modes (air, terrestrial, and water) that facilitate connection between continents, difficulties inherent to identification of potentially problematic species, and for aquatic systems, insufficiently regulated aquarium and ornamental pond industries. In this study, we aimed to assist traditional species identification methods with genetic methods and provide ways of verifying the status of alien plants (invasive or non-invasive) sold in aquarium market in South Africa. To this end, the best DNA barcode for South Africa's freshwater plants was identified; a DNA barcode library was assembled and aquarium plants sold in Johannesburg (South Africa) were screened using this DNA barcode. We found that trnH-psbA was a reliable single DNA barcode for freshwater plant species in South Africa. We therefore assembled a trnH-psbA library on BOLD (Barcode Of Life Database) to assist in future identification of unknown or taxonomically doubtful freshwater alien plants in South Africa. Using this region to screen aquarium species, we found surprisingly that some prohibited aquatic invaders are already in circulation in the local aquarium trade, including Hydrilla verticillata (L.f.) Royle, Egeria densa Planch., Myriophyllum spicatum L., and Echinodorus cordifolius (L.) Griseb. This raises concern and calls for a strict regulation of species traded in aquarium industries to be implemented, as well as a need for public environmental education on the threat posed by invasive and potentially invasive plants for South Africa's natural aquatic ecosystems.