[3] The lichen starts out as a granular crust on the rock surface, and develops fruticose stalks, or pseudopodetia, up to 3 cm (1.2 in) tall and about 1 mm thick that have rounded black apothecia at the tips.

In addition to green algae, the lichen contains cyanobacteria that help contribute to soil fertility by supplying fixed nitrogen.

[1] Elias Fries's son Thore Magnus transferred the species to his then newly created genus Pilophorus in 1857.

[9][10][11] Analysis of small subunit ribosomal DNA sequences showed P. acicularis to be more closely related to the Cladoniaceae, rather than the Stereocaulaceae.

[16] The pseudopodetia (upright stalk-like extensions of the thallus made of vegetative tissue) range from 0.5 to 3 cm (0.2 to 1.2 in) high, and are about 1 mm thick; they grow in dense clusters.

Most pseudopodetia are either unbranched or forked into two branches, with the stalks curved so as to appear as if combed; less frequently, they are erect like pins, and up to 1 cm (0.4 in) tall.

Some specimens are highly branched in the upper part of the pseudopodetia, causing them to bear some resemblance to P. robustus, although this morphology is uncommon.

Internally, the pseudopodetia are solid when young, becoming hollow with age, and are composed of long, thin, highly gelatinized hyphae with narrow cavities about 0.5 μm wide.

The algal layer is not continuous—contrasting with lichen species that have thalli that stratify into discrete tissue types, including a photobiont layer—and occurs with the mycobiont in the form of granules.

The generative tissue (hyphae that eventually forms the thallus) is closely interwoven with short, broad cells that have large cavities.

[9] Pilophyllus clavatus, a species found in Western North America, Japan, Taiwan and South Korea, resembles P. acicularis, but it has much shorter pseudopodetia—up to 1.5 cm (0.6 in) long.