Habitat differentiation in the threatened aquatic plant genus Baldellia (L.) Parl. (Alismataceae): Implications for conservation

A comparative analysis of the habitats of Baldellia ranunculoides (subsp. ranunculoides and subsp. repens) and Baldellia alpestris (Alismataceae) was carried out across central and western Europe. Soil samples from 43 populations were analyzed and the composition of accompanying vegetation was analyzed by canonical correspondence and indicator species analysis. Significant differences in the habitat conditions and the accompanying vegetation were found between the three taxa. B. ranunculoides subsp. repens is growing in lowland water bodies on acidic substrates (pH 5–6.3) which are markedly richer in organic matter and poorer in cations, especially in Ca2+. B. ranunculoides s. str. is also a lowland taxon, but grows on more mineral and basic substrates (pH 7–9), usually rich in Ca2+. The endemic B. alpestris grows in the most distinct habitats, on substrates with low pH and with very low Ca2+ concentrations, at much higher altitudes than the other taxa and in very specific plant communities that have almost no affinities with those of the two lowland Baldellia-taxa. The Baldellia-taxa are threatened by eutrophication of their habitats. Moreover, many of the extant populations, in particular those of B. ranunculoides s. str., are very small and will be threatened by environmental stochasticity. Reintroduction and the creation of new populations might reduce the risk of extinction. Information given on the detailed habitat preferences of the Baldellia-taxa could help conservation efforts for these endangered taxa and identify suitable sites for (re-) introductions.