Bolander's map lichen

Bolander's map lichen (Rhizocarpon bolanderi) is a crustose lichen that forms distinctive dark, map-like patches across the surface of exposed rock, a growth habit shared with other members of the Rhizocarpon genus but distinguished here by subtle differences in thallus structure and areolae pattern. It is restricted to high-elevation siliceous boulders and rock outcrops in alpine and subalpine zones of the western United States, where it grows at a notoriously slow pace, often taking decades to expand even a few centimetres. This slow growth, combined with a narrow ecological niche tied to specific rock chemistry and microclimate conditions, makes the species highly vulnerable to any disturbance of its rocky substrate.

Rhizocarpon bolanderi is currently classified as Critically Endangered (CR) by the IUCN, reflecting severe range restriction and the fragility of the isolated populations that remain. Primary threats include alteration of alpine habitat through recreational activity such as climbing and bouldering, which can physically damage or remove colonized rock surfaces, as well as shifting climatic conditions at high elevation that may alter the temperature and moisture regimes the lichen depends on. Because lichens integrate atmospheric conditions directly through their tissues, the species is also sensitive to even low levels of air pollution and nitrogen deposition reaching these remote sites.

On a more encouraging note, the alpine habitats where this lichen persists often fall within protected wilderness areas or national forest land, offering a degree of passive protection from large-scale development, and growing interest among lichenologists in documenting rock-dwelling Rhizocarpon species is improving baseline knowledge that could inform future targeted conservation action. Continued monitoring of known populations and protection of alpine rock communities will be essential to ensuring this slow-growing, long-lived lichen persists.

This crustose lichen species inhabits exposed siliceous rock surfaces, particularly granite and other acidic rocks in montane and subalpine environments. It typically grows on vertical to slightly overhanging rock faces where it receives adequate moisture from fog and precipitation while avoiding excessive water accumulation.