Morphometric and genetic divergence among populations ofNeotinea ustulata (Orchidaceae) with different flowering phenologies

Abstract

The terrestrial orchid speciesNeotinea ustulata has recently been split into two subspecies, differing remarkably in their flowering time, but only slightly in morphological characteristics, which makes their taxonomic status uncertain. We have analyzed morphometric and genetic differences between the early- and late-flowering populations in Central Europe. Our results on morphology are ambiguous. Indirect gradient analysis has not shown a distinct separation of early- and late-flowering individuals in the ordination space. However, according to MANOVA, populations of early- and late-flowering plants can be distinguished by plant height, leaf length, numbers of basal (rosette) and stem leaves and even better by certain ratios of these numbers. All genetic analyses, on the other hand, are definite and consistently distinguish two groups. Random amplified polymorphic DNA (RAPD) markers have shown that the early- and late-flowering populations differ significantly from one another. Principal coordinate analysis (PCoA) based on presence/absence matrix of RAPD bands separated the two groups, implying that the difference in flowering phenology could form an effective barrier to gene exchange. Partitioning of genetic diversity in analysis of molecular variance (AMOVA) has shown that the genetic divergence between the two groups, early- and late-flowering populations, is somewhat greater (33%) than the genetic variability among populations within particular group (23%). Using the Mantel test, we found that genetic differentiation coefficients between populations closely correspond to their geographic distribution. After elimination of the effect of sample origin from the model, direct gradient analysis (RDA) has shown that the early- and late-flowering groups differ significantly in their RAPD spectra. To conclude, our results indicate the presence of two genetically and phenologically distinct taxa, but the weak morphological differentiation supports the taxonomic rank of variety rather than subspecies.