Summary:
Sirotrema pusilla is not likely to be encountered casually, but was described from BC and of intrinsic interest: the Sirotrema species appear to be intermediate between Sirobasidium (not in western North America) and Tremella.

Microscopic:
ballistospores 5.5-7 x 3-4 microns, oblong, flattened adaxially, sometimes slightly curved, germinating by repetition or by budding, blasto-basidiospores cylindric or slightly tapered proximally, produced directly from epibasidium or from an apical cell on epibasidium, often remaining attached and sometimes conjugating with similar cells on adjacent basidia; probasidia 9-12(15) x 6.5-7.5(9) microns, mostly nearly spherical to obovoid, ellipsoid, or subcylindric, "single or sometimes in contiguous pairs, infrequently in chains of 3, predominantly 4-celled at maturity, but a few appearing irregularly 1-3 septate, the meiospores disposed diagonally or in a linear series (i.e. transversely septate basidia)", epibasidia "5-75 x 1.5-2 microns, slightly swollen apically, infrequently septate below the apex, the terminal cell 5-6 x 1.5-2 microns and producing blastospores"; in young fruiting bodies, "hyphae compact, of short segments, 1.5-2.5 microns between clamps, swollen at the clamps to 4-5 microns", in more mature fruiting bodies, "segments elongated, infrequently branched, the branches arising through clamps or directly from hyphae", haustorial branches present, often with 2 filaments (1 basal, 1 terminal), or a single initial filament branching near the parent cell, occasional vesicular swellings up to 20 microns in diameter present in context and in subhymenium; haploid state a yeast

Notes:
includes BC

Synonyms and Alternate Names:
Cordyceps variabilis Petch
Cordyceps viperina Mains