Saxicolous on andesite cliff face above deep chasm. Thallus up to 20 mm diameter (usually less), upper surface pale greyish-white, conspicuously white-pruinose, lower surface and margins densely covered in black rhizinomorph felt (rhizinomorphs protruding along thallus margins). Fits this species well except that all material seen had apothecia. Galloway (2007) notes 'an absence of apothecia' is diagnostic of this species or did he mean he hadn't seen any? Either way this is the best name I can come up with for this common high alpine Umbilicaria on Mt Ruapehu. See also: https://inaturalist.nz/observations/3085088 Galloway, D.J. 2007: Flora of New Zealand; Lichens, including lichen-forming and lichenicolous fungi. Revised second edition.1 ed. Lincoln, Manaaki Whenua Press. 1006 p.