Four new Western Australian species related to Hibbertia axillibarba (Dilleniaceae)

Hibbertia axillibarba was described in 2000 as a short-range endemic species known only from South Ironcap, a semi-arid, banded ironstone hill in the Western Australian southern Goldfields. Subsequently, several specimens collected from sandplain habitats in the Western Australian wheatbelt, varying from close to, to distant from, South Ironcap, were determined as H. aff. axillibarba or H. cf. axillibarba at the Western Australian Herbarium. Close study of these specimens has shown that none matches H. axillibarba, which on current knowledge remains endemic on South Ironcap; instead, they comprise three distinct species, which are described here as Hibbertia arenicola K.R.Thiele, H. erioclada K.R.Thiele and H. elachophylla K.R.Thiele & T.Hammer. A fourth new species, H. lanulipes K.R.Thiele, is included in this paper as it is likely to be related to the others, despite being morphologically quite different from them. None of these species is widespread and some are likely to be rare and restricted.