Cortinarius albocyaneus is proposed for assessment because it is a specialist ectomycorrhizal fungus strongly associated with Helianthemum in calcareous grasslands, forming part of a recognised guild of Cortinarius species linked to Helianthemum hosts in Great Britain ScienceDirect. This guild occupies highly fragmented microrefugia—small patches of thin, base‑rich soils that have undergone long‑term decline through agricultural intensification, nutrient enrichment, scrub encroachment, and loss of traditional management.

Although C. albocyaneus is widespread across the Northern Hemisphere in a broad sense GBIF, its Helianthemum‑associated grassland niche is extremely restricted, and records from these habitats are scarce. This reflects both genuine rarity and chronic under‑recording of ECM fungi in open grassland systems. The species shows a split habitat profile, occurring in both calcareous grasslands and certain light deciduous or mixed woodlands, but the grassland component is the one undergoing the most severe decline, making its persistence in these microrefugia uncertain.

As an ECM fungus dependent on stable host populations and intact soil chemistry, C. albocyaneus is highly sensitive to nitrogen deposition, hydrological change, and soil disturbance. Loss of calcareous grassland directly reduces the availability of suitable host‑root zones, and fragmentation limits gene flow, increasing the risk of local extirpation. Given the ongoing contraction of Helianthemum grasslands and the species’ reliance on these habitats, C. albocyaneus fits the profile of taxa likely to meet B2ab(iii) due to continuing decline in habitat quality and extent.

For these reasons—ecological specialisation, habitat fragmentation, declining microrefugia, and sensitivity to environmental change—Cortinarius albocyaneus merits formal Red List assessment.