Is Nymphaea lotus var. thermalis a Tertiary relict in Europe?

Abstract

Nymphaea lotus L. is a tropical and subtropical species of waterlilies with an African distribution. A conspicuous satellite occurrence can be found in Europe in a thermal spring in NW Romania. This population (treated as var. thermalis (DC.) Tuzson) received much attention as a potential Tertiary relict in the flora of Europe, although its relict vs. planted nature has been part of great debate among scholars during the last 200 years. We revisit this question by using molecular phylogenetic methods to estimate the timing of divergence of this species, and put this population into a phylogeographic context by comparing it to samples coming from the whole area of the species. By using sequences of the nuclear and the plastid genome, we reconstructed the phylogeographic relationships within N. lotus with a haplotype network building approach, that identified a genetically distant lineage in western Africa, which we relate to N. zenkeri Gilg, the sister species of N. lotus. All the populations of N. lotus s.str. displayed genetic distance between each other except for the Egyptian and Romanian populations. On our dated phylogeny of the subgenus Lotus the separation between N. lotus and its sister species was found to be younger than the end of the Tertiary (1.26 Mya). These results clearly refute the Tertiary relict status of the European population of N. lotus.