Lemon Myrtle' is becoming increasingly popular in Europe both for use in cuisine and phytotherapy. However, this common name covers two completely diVerent species, Backhousia citriodora F. Muell. and Leptospermum citratum Challinor, Cheel & A.R.Penfold. These species diVer with respect to secondary compounds and even can cause, if mixed up and applied in high dose, toxic eVects. We describe how the two species can be discriminated microscopically making use of diVerences in the morphology of leaf pavement cells and the relative size of palisade parenchyma. Based on the large subunit of ribulose-1,5-bisphosphate carboxylase oxygenase (rbcL) as molecular marker, the phylogenetic position of the two species within the Myrtaceae could be clariWed. This sequence information was used to develop a simple assay to discriminate the two species even in dried and highly fragmented mixtures as typically occurring in commercial samples. This assay utilises the occurrence of single-nucleotide exchanges between those species that produce diVerent fragments when the rbcL ampliWcates are restricted with Sac II.
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