Summary:
Features include minute, whitish cups that are pruinose on the disc and downy on the exterior, growth on pyrenomycetes, and microscopic characters including branching paraphyses.
Polydesmia pruinosa is found in BC, WA, and also NY, PA, TN, Canary Islands, and Madeira; it is common and widespread in the United Kingdom and Europe on many different pyrenomycetes; it can be common in the Pacific Northwest, but is rarely collected, (Korf).
Upper surface:
rarely exceeding 0.05cm, whitish, spore-bearing upper surface distinctly pruinose under a hand-lens, (Korf), 0.03-0.05cm, turbinate to cushion-like, spore-bearing surface white and farinose (from projecting paraphyses); margin white and finely felty, (Breitenbach)
Underside:
white to dirty white; downy under a hand lens, (Korf), white; finely felty, (Breitenbach)
Stem:
with short stem or stem nearly absent, (Korf), without a stem (Breitenbach)
Microscopic:
spores (13.9)14.6-20.5(22.0) x 3.7-5.1 microns, "often slightly curved, shorter at the ascus apex, longer toward base of ascus", aseptate at first, soon 3-septate (evident in KOH-phloxine-glycerine or lactic acid - cotton blue, but many authors have failed to see septa); asci (78)80-110 x (8.0)8.8-10.2(11.0) microns, with pore blue in Melzer''s reagent; paraphyses filiform but apically deformed and propoloid, (Korf), spores 15-21 x 4-4.5 microns, elliptic-fusiform, sometimes slightly bent, smooth, colorless, usually with 4 droplets, biseriate, sometimes with indistinct septum; asci 8-spored, 105-120 x 11 microns, positive reaction in iodine; paraphyses filiform, cylindric, and strongly forked at tips, (Breitenbach)
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