Known for its distinctive rosette-like thallus with surface patterns, S. firmula exemplifies the morphological and ecological adaptations characteristic of the genus Saxiloba, for which it is the type species.

[4] In 2020, Robert Lücking, Bibiana Moncada, and Harrie Sipman transferred the species to the newly created genus Saxiloba based on its unique placodioid thallus morphology and molecular phylogenetics evidence.

A loosely arranged medulla of fungal hyphae underlies the photobiont layer, and a dark hypothallus anchors the lichen to its rocky substrate.

[5] Saxiloba firmula is found in the Caribbean, including Cuba, Isla de la Juventud (formerly Isle of Pines), Puerto Rico, and the Bahamas.

[5] The species' vertical arrangement of crystal clusters and algal cells within its thallus may enhance its ability to capture and utilise light in low-light environments.