| Summary: | Knowledge of phylogenetic relatedness and cytogenetic characteristics can facilitate breeding programs and interspecific hybridization in ornamentals. In this study genetic relationships, genome sizes and chromosome numbers were determined in a collection of 82 lavender genotypes, including 15 hybrids. Amplified Fragment Length Polymorphism (AFLP) marker analysis revealed 5 clusters, corresponding to the sections <i>Lavandula</i>, <i>Stoechas</i>, <i>Dentatae</i>, <i>Pterostoechas</i> and <i>Subnudae</i>. Genome sizes varied between 0.76 ± 0.02 pg 2C<sup>−1</sup> and 4.80 ± 0.06 pg 2C<sup>−1</sup> and chromosome numbers ranged from 2n = 22 to 2n = 100. Genome sizes of hybrids were intermediate to the progenitors genome sizes. All analyzed hybrid genotypes were characterized by even chromosome numbers, with 2n = 48 or 50. Using Principal Coordinate Analysis (PCoA) separate hybrid clusters were identified between the progenitor species clusters. Polyploidy and/or aneuploidy was observed in two hybrids genotypes: <i>L</i>. × <i>intermedia</i> ‘Heavenly Angel’ (2n = 100) and <i>L</i>. × <i>heterophylla</i> ‘Big Boy James’ (2n = 66). Results obtained in this study can be used to predict cross compatibility among different species, thus enabling targeted breeding towards the creation of new improved <i>Lavandula</i> cultivars.
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