[1] It is found in the mountainous forests of northern Thailand and in Tamil Nadu, India, where it grows in humid habitats in association with mosses.

The type specimen was collected by the authors from Doi Inthanon (Chiang Mai) at an altitude of 2,450 m (8,040 ft); there, on a roadside near the summit, the lichen was found growing amongst bryophytes that had fallen from the canopy.

Towards the tip, the lobes produce smaller lobules that break down somewhat to resemble soralia; this may be an adaptation to the wet growth conditions in its environment.

Apothecia are rare in this species; if present, they are up to 1.5 mm in diameter and have a dark brown disc and a thalline margin with a squamulose form.

[2] Fuscopannaria siamensis is muscicolous (associating with mosses), and occurs in moist forests and the light-exposed edges of evergreen savannahs.