Attempt of a morphological differentiation of Helleborus species in the Northwestern Balkans

The genus Helleborus is represented in the Northwestern Balkans by 8 species. Some of them (H. atrorubens, H. foetidus (newcomer, introduced as well as escaped from culture), H. niger, and H. orientalis (newcomer, escaped from culture)) are rather easy for determination and discrimination. While other 4 species (H. dumetorum, H. multifidus, H. odorus, and H. viridis) are really difficult for determination because of their narrow morphological similarity, which also is realized a wide variety in leaf shape. The distribution areas of last 4 species overlap in the Northwestern Balkans, so that there are no really clear borders of their distribution. Dominating species in this region is H. multifidus, and especially common there is its subsp. istriacus. Other 3 species are rare and are therefore often overlooked and the herbarium specimens are frequently misidentified as H. multifidus. Moreover, all these 4 species produce number of hybrids, and as a result all kind of transistions between these taxa could be found. In particular, 11 hybrides could be confirmed for this region. The hybrid between H. dumetorum and H. multifidus is described here as Helleborus ×mucheri.