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Usnea praetervisa (Asah.) P. Clerc
Family: Parmeliaceae
Usnea praetervisa image
Philippe Clerc  
Thallus: erect-shrubby, up to 2-6 cm long branching: anisotomic- to isotomic-dichotomous basal part: jet black to brownish black branches: tapered; lateral branches: not narrowed at attachment points segments: terete or sometimes slightly ridged, cylindrical papillae: few to numerous, verrucous, principally on main branches tubercles: few, irregularly distributed fibercles: numerous on terminal branches, looking like pseudocyphellae, coalescing together, frequently evolving into soralia fibrils: few to numerous, ┬▒regularly distributed, short (< 3 mm); and slender soralia: minute, irregular, without a reflexed edge, smaller than half of the diameter of the branch, arising mainly on fibercles, even and plane, frequently fusing together and looking like a large soralium, generally numerous, sometimes covering entirely the terminal branches isidiomorphs: short and spinulous, numerous especially on young soralia but present on mature soralia as well pseudocyphellae: absent cortex: thin to moderately thick (6-10%), dull to shiny, medulla: usually thin, dense to compact, sometimes peripherally orange pigmented axis: thick, non pigmented Apothecia: not seen Spot tests: K+ dull yellow turning reddish orange, C-, KC-, P+ deep yellow Secondary metabolite: norstictic acid (major). Substrate and ecology: mainly on bark of Quercus spp. near the coast between 200 and 500 m or inland in the mountains on Quercus hypoleucoides at intermediate elevations World distribution: Eurasia and North America Sonoran distribution: southern California, especially the Channel Islands. Notes: Morphologicaly U. praetervisa is difficult to separate from U. subfloridana. The latter species has soralia with slightly reflexed margins (50x!) producing a cortical rim that well delimits the soralia, that develop initially on the cortex. These soralia become shortly stipitate, slightly convex at the top and usually remaining separate. In contrast, U. praetervisa has ┬▒diffuse soralia, unstipitate, developing on fibercles and coalescing together. The diameter of the soralia is smaller and the density of the soralia is on average higher in U. praetervisa than in U. subfloridana. Anatomicaly, U. subfloridana has a tendency to have a thicker cortex and a thinner central axis than U. praetervisa. Chemicaly, U. praetervisa has norsticitc acid in the medulla whereas U. subfloridana produces thamnolic and/ or squamatic acids.