Thailand. Chiang Mai Province: Doi Suthep-Pui, Bhu Bing Palace, 1400 m, 18 October 2020, S. Chantanaorrapint & O. Suwanmala 4077 (holotype: PSU!; isotype: BKF!, NICH!).

Phaeocerosperpusillusvar.scabrellus is similar to the autonimic variety but differs in nearly smooth spores under light microscope (or vermiculate under SEM), whereas the autonimic variety have pluripapillae on the distal surface and vermiculate on the proximal.

Thallus yellowish-green to dark green in fresh material, dull green to blackish- brown in dry material, prostrate or moderately adhering to the substratum, solid, ecostate, orbicular to sub-orbicular, dichotomously branched into several lobes, with a smooth dorsal surface; lobes ensiform or sometimes fan-shaped, up to 0.8 mm long, 1–3 mm wide; margins wavy, nearly entire to shallowly crenulate; apex flat, rarely ascending, occasionally tapering into apical tubers; tubers sometimes present on ventral surface. Thallus in cross section plano-convex to concave-convex, 4–10 cells thick in the middle region, without mucilage cavities. Dorsal epidermal cells rectangular to heptagonal, 28–75 × 25–50 µm, thin-walled, smooth. Chloroplast one per cell, large, occupying almost entire cell, variable in shape; pyrenoid present. Nostoc colonies scattered through the ventral side of thallus, appearing as dark dots. Rhizoids hyaline or pale brown along ventral surface, inner wall smooth or tuberculate. Sexuality monoicous. Androecia scattered and slightly raised over the dorsal surface of thallus, 2–3 antheridia per chamber; antheridia subglobose to globose, exposed at maturity, irregularly arranged jacket cells, shortly stalked, stalk with quadriseriate cells. Archegonia embedded in thallus, connected to the upper surface, scattered near the lobe of thallus. Involucre solitary, conical-cylindrical, up to 2 mm long, 2–4 cells thick, mouth smooth to crenulate. Sporophytes capsule somewhat inclined, stout to narrowly cylindrical, 0.5–1(–1.2) cm long, yellow at apex, dehiscing from top toward base, bivalves rarely twisted when dry; epidermal cells of capsule elongate-rectangular, 68–200 × 12–30 µm, thick-walled, stomata present with two reniform guard cells, surrounded by 5–8 epidermal cells; assimilative layers 3–6 cells thick in cross section; the innermost capsule cells dark brown, subquadrate to rectangular; 27–67 × 22–53 µm; columella well-developed, red-brown, consisting of 16 cells (4 × 4 lines of cells) in cross section. Spores unicellular, yellow, rounded-triangular in polar view, equatorial diameter 32–50 µm in diameter, nearly smooth under light microscope (LM), proximal surface with a distinct trilete mark, bordered by vermiculate strip on each side of trilete mark, each facet covered with fine vermiculate pattern; distal surface with a slightly dome-like region at the center, more densely vermiculate than proximal surface, sometimes with minute granules. Pseudoelaters light brown or yellowish-brown at maturity, thin-walled, occasionally branched; pseudoelater cells subquadrate to short rectangular, 30–45 × 25–30 μm, without helicoidal band.

The epithet of the variety refers to scabrate ornamentation observed under light microscope.

Phaeocerosperpusillusvar.scabrellus is currently known only from northern Thailand. It grows on disturbed soil and sandstone in open site in grassland, pine-oak mixed montane deciduous forests at elevation of 1390–2100 m. It may grow associated with other bryophytes such as Anthocerossubtilis Steph., Notothylaslevieri, N.orbicularis (Schwein.) Sull. ex A.Gray, and P.carolinianus.

This variety is currently known from three subpopulations, which are in protected areas (Chiang Dao Wildlife Sanctuary and Doi Suthep-Pui National Park). One of the subpopulations is located in a camping area, which is a common visiting site for tourists and dominated by Ageratinaadenophora (Spreng.) R.M.King & H.Rob. (invasive species). Therefore, habitat quality is threatened by trampling and other destructive activities potentially caused by regular visits by tourists to the area, and invasive plant species. Together, these have the potential to cause a population reduction. The other subpopulation is also somewhat disturbed by human activities such as shifting cultivation. The extent of occurrence (EOO) of P.perpusillusvar.scabrellus is estimated to be 262.925 km² and its area of occupancy (AOO) is estimated to be 12 km², which falls within the limits for Endangered status under criterion B1 and B2 of IUCN Red List Categories and Criteria. Conservation efforts should focus on implementing strict regulations to reduce the impact of human activity and controlling invasive species, while also raising awareness among local communities about the importance of protecting the habitat.

Thailand. Chiang Mai Province: Chiang Dao Wildlife Sanctuary, 1700–2000 m, 1 November 2013, S. Chantanaorrapint & C. Promma 3125B, 3129, 3216 (PSU); Doi Suthep-Pui National Park, Doi Mon Long Viewpoint, 1390 m, 4 November 2015, S. Chantanaorrapint & W. Juengprayoon 143B (PSU); 15 November 2020, S. Chantanaorrapint & O. Suwanmala 4089, 4090 (PSU); Bhu Ping Palace, 1400 m, 8 September 2013, S. Rattanamanee 3 (PSU); 18 October 2020, S. Chantanaorrapint & O. Suwanmala 4077 (PSU); 5 October 2021, S. Chantanaorrapint & O. Suwanmala 4116 (PSU).