Long neglected diversity in the Accursed Mountains of northern Albania: Cerastium hekuravense is genetically and morphologically divergent from C. dinaricum

The Balkan Peninsula is a hotspot of European biotic diversity. One of its biogeographically most peculiar but poorly explored regions are the Albanian Alps (Alpet Shqiptare/Prokletije/Accursed Mountains) on the border between Albania, Kosovo and Montenegro, characterised by a high number of endemic species. A poorly known taxon from the Albanian Alps is Cerastium hekuravense, which was described from Mt. Maja Hekurave (Albania) in 1921, but later usually merged with C. dinaricum, a widespread endemic of the Dinaric Mountains, or connected with the arctic-alpine C. alpinum. Here, we used amplified fragment length polymorphisms to explore the phylogenetic position of C. hekuravense and particularly its relationship to C. dinaricum. Our data show that both species are genetically well differentiated, but their relation to other taxa remains unclear—they are either closely related to Alpine species of C. ser. Latifolia or to species co-occurring on the Balkan Peninsula, such as C. banaticum and C. decalvans. In addition, multivariate morphometric analyses show that C. dinaricum and C. hekuravense are morphologically well differentiated. Also their relative genome sizes, estimated using flow cytometry, differ. We propose a taxonomic treatment with lectotype designation for both taxa and provide descriptions and an identification key. Last but not least, these cold-adapted species mostly growing on northerly exposed humid screes are highly threatened due to the global warming and should be ranked endangered according to IUCN criteria. Cerastium hekuravense known only from three localities is likely one of the most endangered mountain plant species of the Balkan Peninsula.