Peltigera cinnamomea forms a specialised symbiotic relationship with specific strains of the cyanobacterium Nostoc, enabling it to fix atmospheric nitrogen, crucial for survival in nutrient-poor environments.

The type specimen of Peltigera cinnamomea was collected by the Canadian lichenologist Trevor Goward on 13 April 1985, within the Clearwater River Basin in British Columbia (Canada), at an elevation of 675 m (2,215 ft).

[2] It did not, however, meet the specific standards for valid publication of a new species, due to non-compliance with Articles 39.1 and 40.1 of the nomenclatural rules, which require a clear description and the designation of a type specimen.

Peltigera cinnamomea, although readily recognisable in its natural habitat, was historically misidentified as P. praetextata, because both species share some superficial similarities.

[5] Early (2003) molecular phylogenetics studies of taxa within the P. canina species complex delineated two major monophyletic groups, meaning they consist of all the descendants of a common ancestor, each with distinct ecological preferences.

The acronym CICADE stands for "Cinnamomea, Canina, Degelii, and their close relatives", encompassing species that are primarily mesophytic, meaning they thrive in moderately moist environments, to subhygrophytic, indicating they prefer slightly wetter conditions.

The lobes of this lichen are somewhat leathery and stiff, measuring approximately 1 to 3 cm (0.4 to 1.2 in) in width, elongating and loosely overlapping with irregular branches.

The rhizines, root-like structures, match the colour of the veins and range from simple to intricately branched (penicillate), enhancing the lichen's attachment to its substrate.

[4] Peltigera cinnamomea forms a specialised symbiotic relationship with the cyanobacterium Nostoc, which serves as its primary photosynthetic partner (photobiont).

Genetic studies have identified specific clusters of Nostoc, indicating a closely adapted relationship where the lichen's fungal component and its photosynthetic partner have co-evolved to maximise mutual survival benefits.

This partnership benefits P. cinnamomea by enabling it to efficiently fix atmospheric nitrogen, vital for thriving in nutrient-sparse environments.

This tailored relationship suggests that the distribution of P. cinnamomea may be closely tied to the presence of its specific Nostoc partners, reflecting a delicate balance between the lichen and its preferred photobiont environments.

Both species occur throughout inland British Columbia, but P. cinnamomea predominantly inhabits areas with prolonged snow cover, persisting until May or June, conditions under which P. praetextata is absent.

[4] Within the genus Peltigera, P. cinnamomea is grouped with species that feature Nostoc as a primary photobiont and have an appressed laminal tomentum.

Though termed an "order", this classification groups ecosystems with similar species and interactions, typical of valley bottoms and lower slopes across northwestern North America.

Influenced by Pacific air masses, these areas benefit from moist conditions and extensive snow cover, providing a stable environment for the growth of species like P. cinnamomea.

[12] Peltigera cinnamomea has an "S5" provincial conservation status in British Columbia, meaning it is "demonstrably widespread, abundant, and secure".