Özet:

Onopordum hasankeyfense Pınar & Behçet (Asteraceae: Cardueae) from south-eastern Anatolia, Turkey, is described. This species grows on the rocky slopes beneath the Hasankeyf castle in the Hasankeyf District (C8, Batman province). Morphologically, the new species is related to Onopordum anatolicum (Boiss.) Boiss. & Heldr. ex Eig, a species endemic to central and western Anatolia, and O. acanthium L. This new species differs from the others in its indumentum, capitulum shape, phyllary colour and shape, unequal corolla lobes, and pappus. The ecology and phenology of the new species, as well as its etymology and diagnostic features, are presented and discussed. Images of the new species are provided and compared with O. anatolicum and O. acanthium. In addition, the pollen characteristics and achene features of the species were examined using both light and scanning electron microscopy. The conservation status of O. hasankeyfense was assessed according to IUCN criteria. A distribution map of O. hasankeyfense and related species is also presented.

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