Originally discovered in Hawaii in 2007, G. pacificus has since been found in various locations across the Pacific, including Australia, New Caledonia, Vanuatu, the Philippines, and Japan.

Initially, its taxonomic classification was uncertain,[1] but recent discoveries of specimens with sexual reproductive structures (perithecia) have enabled scientists to confidently place it within the family Porinaceae.

The type specimen of Gallaicolichen pacificus was originally collected from Kolukola Park in Hamakua, Hawaii, where it was found growing on Syzygium cumini.

However, the discovery of fertile specimens in New Caledonia, producing both peltidiangia and perithecia, along with molecular analysis using the mitochondrial small subunit ribosomal RNA (mtSSU) marker, has confirmed its placement within the family Porinaceae.

The thallus is relatively thin, measuring up to 20 μm, and comprises an interlaced network of fungal filaments (hyphae) and large, organized algal cells that form the lichen's photosynthetic component, known as the photobiont.

These peltidiangia begin to develop at the centre of the patch and are almost perfectly circular, featuring a relatively thick, upright margin that is white and composed of raised hyphae that are not fused together.

Typically, one to two ends of fungal filaments are found between the branches of the algal cells and are visibly apparent on the outer surface of the propagules.

The involucrellum (a protective outer layer) is fused with the excipulum (the wall of the fruiting body), and both are densely covered with smaller crystals measuring 10–15 μm thick.

[3] In addition to the type locality in Hawaii, Gallaicolichen pacificus has been recorded from Queensland, Australia, New Caledonia, Vanuatu,[2] the Philippines,[4] and Japan (Ryukyu Islands).