Phlyctis subargena

The thallus is crustose and thin (about 60–120 μm thick), forming greenish-white patches on bark. Its surface is uneven and has a somewhat cobwebby or felty texture, and it often breaks into small, irregular areoles about 0.1–0.2 mm across; a white prothallus may be visible at the margins and in cracks. The soralia are usually paler than the surrounding thallus and produce abundant powdery to granular soredia; neighbouring soralia may merge into diffuse, irregular patches.^[2]

Apothecia (fruiting bodies) are common and minute (about 0.1–0.3 mm wide), usually occurring in clusters of 3–8 (occasionally up to 10) and partly immersed within sorediate thallus patches. The disc is reddish-brown, flat to slightly irregular, and usually dusted with white pruina; the exciple (rim) is weakly developed. Microscopically, the spore-bearing asci are broadly club-shaped and two-spored (110–150 × 32–40 μm). The colourless spores are muriform (divided by many cross-walls), measuring 42–78 × 30–42 μm, and show no iodine reaction (I−). The photobiont (photosynthetic partner) is a green alga with spherical cells 12–18 μm in diameter. In spot tests the cortex is K+ (yellow) and C−, while the medulla is K+ (yellow–orange–red), C−, and PD+ (yellow). Thin-layer chromatography detected norstictic acid as the major lichen product.^[2]

Phlyctis subargena is a corticolous (bark-dwelling) species, known only from its type locality in Qiujiaba, Wenxian County, Longnan, in Gansu Province, China. Collections in the type series were made on bark at about 2,350–2,450 m elevation during July and August 2007. As of its original description, the species had not been reported from elsewhere, so its wider range and ecological requirements remain poorly documented beyond the locality data available in the original report.^[2] Phlyctis subargena is one of five Phlyctis species that had been reported from China before a 2022 overview added P. subhimalayensis as a new national record.^[3]