Telopea 13(1–2) 285–294 © 2011 Royal Botanic Gardens and Domain Trust ISSN0312-9764 Evidence for the hybrid origin of Nymphoides montana Aston (Menyanthaceae) Nicholas P. Tippery 1 and Donald H. Les Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut 06269-3043 USA 1 Author for correspondence: nicholas.tippery@uconn.edu Abstract Nymphoides is a genus of approximately 50 species worldwide, and arguably achieves its greatest diversity in tropical northern Australia, where most of the 20 native species occur. Species found at temperate latitudes are restricted to the eastern half of the country; of these, three (N. crenata, N. geminata, N. indica) also occur in the tropics, and two (N. montana and N. spinulosperma) are only temperate. During an ongoing phylogenetic study of the genus, DNA sequences from N. montana were a major source of incongruence between phylogenetic trees derived from nuclear (nrITS) and chloroplast (rbcL, trnK) data matrices. Our phylogenetic analysis revealed that N. montana resolved variously with N. geminata (nuclear data) and N. spinulosperma (chloroplast data), which despite their strong morphological similarity, are not closely related to each other. These results indicate a hybrid origin for N. montana, which subsequently retains evidence of its maternal lineage in the chloroplast genome, whereas nuclear DNA markers (nrITS data) have been converted to resemble the paternal lineage exclusively. Introduction Nymphoides Ség. (Menyanthaceae) includes approximately 50 species worldwide and generally is characterised by a submersed rhizome and floating leaves that support clusters or lax racemes of pentamerous flowers (Tippery et al. 2008). Most of the 20 Australian species are exclusively tropical, but several are found in the southeast (Jacobs 1992; Aston 2003, 2009). Two species (N. montana Aston and N. spinulosperma Aston) occur only at temperate latitudes; both were described recently by Aston (1982, 1997) as part of her thorough study of Australian Nymphoides. Morphologically, these species are quite similar to each other and also to N. geminata (R.Br.) Kuntze, a rather widespread species and one of the first Menyanthaceae to be catalogued from the continent (Brown 1810). Nymphoides geminata, N. montana, and N. spinulosperma share the yellow flowers and expanded inflorescence habit that characterise the informal ‘geminata group’ to which they were assigned by Aston (1982, 1997). However, the three species differ from each other by their seed morphology, which Aston (2003) considered to