New publications on plants

Two new publications from the Les lab on Elatine, a genus of aquatic plants:

1. Razifard, H., D. H. Les & G. C. Tucker. 2017. Reticulate evolution in Elatine L.(Elatinaceae), a predominantly autogamous genus of aquatic plants. Systematic Botany 42: 87-95. pdf

Abstract reads: The study of hybridization in aquatic plants is complicated by rarity of flower production, absence of roots, and asexuality. Elatine is a cosmopolitan genus of aquatic flowering plants with about 25 species worldwide. Historically, there has been little concern regarding hybridization in the genus due to the prevalence of autogamy (i.e. self-pollination), which potentially limits xenogamous pollen transfer among the species. Two morphologically complex species (Elatine hexandra and E. americana) are the only known polyploids in the genus. In previous phylogenetic analyses, both species resolved incongruently in gene trees obtained from nuclear (ITS) versus plastid (matK/trnK and rbcL) regions. Suspecting that the phylogenetic incongruence might be a consequence of past hybridization events, we tested that hypothesis by conducting an additional phylogenetic analysis of Elatine, which incorporated sequences from a low copy nuclear gene (phyC). Elatine hexandra and E. americana were the only Elatine species exhibiting intraspecific polymorphic sites, i.e. heterozygosity, in phyC. Allele specific amplification enabled us to resolve these polymorphisms for inclusion in a phylogenetic analysis along with the monomorphic phyCsequences within species obtained for the remaining Elatine species. The phyC tree confirmed that both polyploids probably are allopolyploids, in a pattern consistent with the placement of the putative parental taxa in previous phylogenetic analyses of ITS, matK/trnK,and rbcL sequence data. The distributions of E. americana and E. hexandra, along with their potential parental species, are consistent with the proposed hybrid origins for the polyploids and provide additional clues on their geographic regions of origin.

2. Razifard, H., A. J. Rosman, G. C. Tucker & D. H. Les. 2017. Systematics of the cosmopolitan aquatic genus Elatine. Systematic Botany 42: 73–86. pdf

Abstract reads: The cosmopolitan genus Elatine (Elatinaceae) includes about 25 aquatic species of mostly diminutive aquatic plants, whose relationships have not been evaluated using a phylogenetic approach. The taxonomic study of this group has been complicated by the small stature of the plants, their minute reproductive structures, and their cosmopolitan distribution. Consequently, much uncertainty exists with respect to species delimitations, their geographical distributions, and interspecific relationships. To clarify the infrageneric classification of Elatine and to provide insights on interspecific relationships within the genus, we conducted a phylogenetic study of nearly all (24) of the currently recognized species using both morphological and molecular data. The tree topology obtained based on morphological data (including vegetative and reproductive characters) was less-resolved than the trees based on molecular data, derived from either nuclear (ITS) or two plastid regions (matK/trnK and rbcL). However, the tree topology obtained from combined morphological and molecular data was well resolved and placed the morphologically distinctive E. alsinastrum as the sister group of the remaining species, which fell within two major clades: a clade of 4-merous-flowered species and a clade of 3-merous species, within which was embedded a subclade of 2-merous species. Although a number of topological differences occurred between the ITS and plastid tree topologies, significant incongruence was observed only for the placements of E. americana and E. hexandra, possibly resulting from reticulate evolution. Bergia, the sister genus of Elatine, comprises larger species, which often are mostly helophytic but never truly aquatic. Ancestral state reconstructions based on the ITS tree indicated that a morphological reduction series (in stature and floral merosity) exists among Elatine species, which is best explained as a consequence of adaptation to their aquatic life. These phylogenetic analyses also have helped to clarify the infrageneric classification of the genus and to provide a better understanding of the natural and nonindigenous distributions of the species. The new monotypic section Elatine sect. Cymifera , including E. brochonii, is described.