Taxonomic significance of achene morphology of selected Rosa taxa (Rosaceae) occurring in Poland

Achenes of roses were rarely studied and the studies were focused on anatomical research, mainly on pericarp structure and its development. We investigated the achene morphology by light- and scanning electron microscopy (LM and SEM) of 17 Rosa taxa from three sections (R. gallica from Gallicanae section, R. pendulina and R. rugosa from Rosa section, and R. agrestis, R. canina, R. canina var. corymbifera, R. dumalis, R. dumalis var. caesia, R. inodora, R. jundzillii, R. micrantha, R. rubiginosa, R. sherardii, R. ×subcanina, R. tomentosa, R. villosa, R. zalana from Caninae section). Eight quantitative and eight qualitative features were examined based on 9181 achenes, in total. Average achene size ranged from 4.37 to 5.39 mm in length and from 2.57 to 3.32 mm in width. The lowest morphological variability among the examined taxa was found in R. canina var. corymbifera, and the highest in R. gallica, R. inodora, and R. sherardii. The most diagnostic features of the achenes studied were suture (visible or invisible), presence or absence of hairs, hairs distribution and density, the exocarp sculpture and cuticle pattern type (we have distinguished four exocarp sculpture and three cuticle pattern types), and length. Qualitative achene features have significantly higher diagnostic value than quantitative ones. Taxonomical value of these features is quite high on the species and section level. Our study has shown that the previously mentioned morphological features of achenes can be used as valuable, additional diagnostic features in delimitation of Rosa taxa at the species and section level. Based on the morphological features of achenes, a determination key for all Rosa taxa studied was created.