Summary:
Hysterangium crassirhachis is characterized by "the brittle peridium, which is easily separable when fresh, and by the tough, rubbery gleba with its large translucent septa which become flinty when dry", (Zeller). Other features include the pinkish color of the fruitbody, the greenish spore mass with cavities radiating from the columella to the peridium, and microscopic characters including smooth fusiform spores on 2-4-spored basidia. It is common among false truffles in the Pacific Northwest (Trappe(13)).

Interior:
gelatinous; from "grayish olive" to "deep grayish olive" when fresh; "cavities radiating from the columella to the peridium, sometimes simple, appearing as linear openings in sections, but usually labyrinthiform, broken by septa jutting out from the columellar branches on either side, not filled", (Zeller), very firm and rubbery; dark olive green, (Trappe, M.(3))

Odor:
"mild to slightly fruity or pungent" (Trappe, M.(3))

Microscopic:
spores 13-22 x 4-8 microns, fusiform [spindle-shaped], short-appendiculate, smooth, colorless to olivaceous in mass, thick-walled, sometimes with one to many droplets; basidia 2-4-spored, 30-50 x 6-9 microns, colorless, with short sterigmata; septa from 85-100 up to 200 microns thick, of interwoven, colorless, highly gelatinized hyphae; peridium 400-500 microns thick, duplex, inner and major part parenchymatous, composed of colorless rhomboidal cells, 8-17 microns in diameter, "with an outer rind of smaller, thin pseudoparenchyma of brownish cells about 25 microns thick"; percurrent branches of columella usually at least 300-450 microns thick, composed of interwoven, highly gelatinized, colorless hyphae; stem consisting of hyphae 2-2.5 microns wide, colorless, more or less parallel and anastomosing, (Zeller), spores 11-15 x 4-5.5 microns, elliptic, smooth; no inflated cells in peridium, (Trappe, M.(3))

Notes:
Hysterangium crassirhachis is found from AK south to the Sierra Nevada of CA and east to MT, (Trappe, M.(3)). It is found from BC to southern CA and ID, (Trappe(13)). Collections were examined from OR, CA, (Zeller). It was recorded from OR by Luoma(1), and (Smith, J.E.(1)), and from WA by Colgan(2).

Synonyms and Alternate Names:
Fomes connatus (Weinm.) Gillet
Polyporus populinus Schumach.: Fr.