Summary: Features include 1) growth on the underside of dead branches and twigs of living fir and hemlock, 2) cushion-shaped, resupinate fruitbodies forming circular light orange-buff patches 0.1-0.3cm across that are separate or confluent, the texture pruinose-pulverulent, the margin at first indeterminate and radiate, lighter in color, cobwebby, becoming more determinate and fairly tightly attached, 3) nearly round spores that are smooth and amyloid, 4) catahymenium containing abundant bottlebrush-like acanthophyses, embedded, ampulliform pseudocystidia, paraphysoids, and emergent basidial elements, and 5) context monomitic without clamp connections.
Microscopic: SPORES (16)18-20(21) x (14)16-18 microns, nearly round, slightly flattened adaxially, smooth, amyloid, thin-walled, apiculate; hyphae "ascending to form a catahymenium" composed of emergent basidial elements, paraphysoids, embedded, ampulliform pseudocystidia, and abundant acanthophyses; BASIDIA 4-spored, at maturity clavate, (75)85-100 x (15)20-24 microns, sterigmata 14-16 microns long, arcuate; hyphal PARAPHYSOIDS scattered, 3-4 microns wide, filiform; PSEUDOCYSTIDIA mostly embedded, (35)75-85(100) x (8)13-20 microns, subcylindric to ampulliform with an apical bulb, contents not darkening in sulphobenzaldehyde; ACANTHOPHYSES variable, mostly cylindric and uniformly thin-walled, rarely swollen in lower part with the basal part thin-walled and generally naked, the aculeate-pronged part covering the top third to half of the element and 4-7 microns wide, acanthophyses colorless to slightly yellowish in KOH, faintly amyloid in Melzer''s reagent; CONTEXT monomitic, composed of hyphae 4-5 microns wide, irregular, branched, with partially thickened walls, simple-septate, (Lemke)
Notes: Acanthophysium abietis has been recorded from BC, OR, ID, NS, ON, PQ, NY, and VT, (Ginns).
Habitat and Range
SIMILAR SPECIES
Acanthophysium farlowii also occurs on conifers and has cylindric, thick-walled acanthophyses and smooth, amyloid spores, but habit is different (disciform with determinate raised margins as opposed to pulvinate with indeterminate adnate margins), habitat is mostly Douglas-fir in the Pacific Northwest, as opposed to fir and hemlock, spores are smaller and oval as opposed to nearly round, basidia are smaller, acanthophyses are wider, and pseudocystidia are flexuous-cylindric (as opposed to subcylindric ampulliform) and never become apically moniliform, (Lemke).
Habitat
on the underside of dead branches and twigs on live trees; Abies balsamea, Abies grandis, Tsuga mertensiana, (Ginns), on the "underside of dead branches and twigs" of living Abies (fir), found also on Tsuga mertensiana (Mountain Hemlock) in the Pacific Northwest, (Lemke)