Hieracium portlandicum (Asteraceae), a new endemic hawkweed from the Isle of Portland, England related to Hieracium leyanum

A new species of hawkweed is described. Hieracium portlandicum differs from H. leyanum, within which it was previously included, in being less hairy, and in having narrower, acute, light greyish-green, less hairy involucral bracts. It is a triploid apomict. Hieracium leyanum is a tetraploid apomict. Hieracium portlandicum is endemic to the Isle of Portland, Dorset, England, where it occurs on Portland Limestone rocks, and on soils derived from it. 103 plants are currently known from two sites, and a comparison against historical data indicates that it is declining. It is ‘Endangered’ under the IUCN Threat Criteria. Some distribution data are also given for H. leyanum which is ‘Vulnerable’ under the IUCN Threat Criteria. A lectotype for H. pollinarium var. platyphyllum on which H. leyanum is based is designated from Wales.