Most RNA editing sites in flowering plant mitochondria are located in coding regions of mRNAs and are usually essential for correct gene expression. Although accordingly little variation should be tolerated, editing sites appear and disappear even between closely related flowering plant species. To investigate whether such editing site variations also occur within species, we analyzed 379 RNA editing sites in the three ecotypes Columbia, Landsberg erecta and C24 of Arabidopsis thaliana. While all editing sites as such are conserved, we identify seven RNA editing sites with 40-60% differences in effective editing between individual ecotypes. These quantitative variations show that the extent of RNA editing in plant mitochondria is very flexible and can change even more rapidly than the evolution of species. The ecotype-specific variations of the RNA editing extent are Mendelian-inherited and can now be used to follow and identify the nuclear loci responsible for these RNA editing phenotypes.