Molecular phylogenetics, seed morphometrics, chromosome number evolution and systematics of European Elatine L. (Elatinaceae) species

Abstract

The genus Elatine contains ca 25 species, all of which are small, herbaceous annuals distributed in ephemeral waters on both hemispheres. However, due to a high degree of morphological variability (as a consequence of their amphibious life-style), the taxonomy of this genus remains controversial. Thus, to fill this gap in knowledge, we present a detailed molecular phylogenetic study of this genus based on nuclear (rITS) and plastid (accD-psaI, psbJ-petA, ycf6-psbM-trnD) sequences using 27 samples from 13 species. On the basis of this phylogenetic analysis, we provide a solid phylogenetic background for the modern taxonomy of the European members of the genus. Traditionally accepted sections of this tree (i.e., Crypta and Elatinella) were found to be monophyletic; only E. borchoni-found to be a basal member of the genus-has to be excluded from the latter lineage to achieve monophyly. A number of taxonomic conclusions can also be drawn: E. hexandra, a high-ploid species, is most likely a stabilised hybrid between the main sections; E. campylosperma merits full species status based on both molecular and morphological evidence; E. gussonei is a more widespread and genetically diverse species with two main lineages; and the presence of the Asian E. ambigua in the European flora is questionable. The main lineages recovered in this analysis are also supported by a number of synapomorphic morphological characters as well as uniform chromosome counts. Based on all the evidence presented here, two new subsections within Elatinella are described: subsection Hydropipera consisting of the temperate species of the section, and subsection Macropodae including the Mediterranean species of the section.

Keywords: Character evolution; Elatinella; Hybridization; Hydropipera; Incongruence; Macropodae; Species delimitation; Waterwort.

Figure 1. Examples of morphological diversity in the genus Elatine.

(A) Habit of the terrestrial form of Elatine alsinastrum (E. subgenus Potamopithys); (B) flowering shoots of water-living form of Elatine alsinastrum; (C) E. brochonii (Spain); (D) E. triandra (Hungary); (E) E. hexandra (Poland); (F) E. californica (USA); (G) E. hungarica (Hungary); (H) E. hydropiper (Hungary); (I) E. campylosperma (Spain); (J) E. gussonei (Lampedusa); (K) E. gussonei (Sicily); (K) E. macropoda (Sardinia). Photographs by A. Molnár V.

Figure 2. Phylogenetic trees reconstructed using the nrITS (A) and plastid (B) matrices.

Both trees are arbitrary chosen MPTs displayed as phylograms with bootstrap support percentages/posterior probability values at the corresponding branches. Dash indicates lack of statistical support, and such branches are indicated by dashed lines. A scale bar representing 20 mutational changes is displayed on both trees, and the abbreviation ‘cl.’ denotes cloned nrITS sequences on the nrITS tree.

Figure 3. TCS-network of cloned nrITS sequences of Polish E. hexandra accessions.

Clone names follow the abbreviated sample name, while the number following it is the indetifier of the clone sequenced. Hypothetical (unrecovered) ribotypes are represented by small circles, and the 22 such ribotypes separating the two ribotype-groups are not represented to keep the figure easily readable.

Figure 4. One of the two MPTs resulted from MP analysis of the combined (nrITS+plastid accD-psaI, psbJ-petA, ycf6-psbM-trnD) sequences displayed as a phylogram (A) and as a cladogram (B).

Next to each branch are bootstrap support values resulting from 1,000 pseudo-replicate followed by Bayesian PP values after the slash.

Figure 5. CVA scatter plot of seed outlines.

Average outlines are presented.