Slideshow image
Placynthium subradiatum (Nyl.) Arnold
Family: Placynthiaceae
[Collolechia subradiata (Nyl.) Szatala,  more]
Placynthium subradiatum image
Matthias Schultz  
Thallus: forming regularly stellate rosettes, up to 1.5 cm across, sometimes forming arcs of up to 2.5 mm, lobate lobes: flat with crenate tips, closely aggregated upper surface: dark olive to brownish, sometimes pruinose lower surface: dark, resting on a thin, inconspicuous, blue-black hypothallus; prothallus: absent Apothecia: semi-immersed to sessile, laminal, lecideine, up to 0.5 mm wide; disc: dark brown to black, open, withou a thalline margin; exciple: thick, dark colored; epihymenium: dark violaceous or dark greenish; hymenium: 50-60 µm high, amyloid; paraphyses: distinctly septate, sparingly branched, apical cells pointed or thickened; subhymenium: light brownish asci: 8-spored, sometimes fewer ascospores: 2-celled, hyaline, ellipsoid, (9-) 11.5-12.5 (-15) x (5-) 6-7 (-8) µm; walls: thin Pycnidia: not seen Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on limestone in moist, montane habitats World distribution: North America Sonoran distribution: moist canyons in central Arizona and Chihuahua. Notes: This is a rather distinct species becasue of its small, regular, stellate rosettes resting on a inconspicuous hypothallus. A similar one is Placynthium asperellum that forms irregularly stellate rosettes resting on a thick, prominent hypothallus.