Summary:
Features include 1) growth in rounded to elongated patches on aspen and other hardwoods, 2) fruitbodies that are pink and whitish-pruinose, bruising dark red, and smooth to tuberculate, 3) a margin that whitish and finely fringed when young to undifferentiated when mature, 4) spores that are slightly allantoid, smooth, inamyloid, and colorless, with a light red spore print, 5) sulfo-positive gloeocystidia that are bladder-like to clavate, 6) richly branched dendrohyphidia covering the hymenium, and 7) a monomitic hyphal system, the hyphae with clamp connections.

Microscopic:
SPORES 8.5-10.5 x 3-4 microns, cylindric, slightly allantoid, smooth, inamyloid, colorless; BASIDIA 4-spored, 35-45 x 5-8 microns, cylindric-clavate, with basal clamp connection, some with secondary septa; CYSTIDIA: gloeocystidia in hymenium up to 90 x 10-20 microns, bladder-like to clavate, sulfo-positive; DENDROHYPHIDIA "strongly branched, on the surface of the hymenium (difficult to observe)"; HYPHAE monomitic, 2.5-3 microns wide, thin-walled to thick-walled, with clamp connections, (Breitenbach), SPORES 9-12 x 2.5-4 microns, cylindric, suballantoid, smooth, colorless, thin-walled, light red in spore print; BASIDIA 4-spored, 40-50 x 5-6 microns, "narrowly clavate with prolonged, intertwined bases", with clamp connection, "old basidia sometimes with adventitious septa"; CYSTIDIA: conspicuous sulfocystidia, total length reaching 100 microns, width 15-25 microns, bladder-like with a stem-like part of varying length, "with granular contents with a strong reaction to sulfovanillin and sulfobenzaldehyde", "hymenial sulfocystidia more or less tube-like", 5-10 microns wide, "some of them pointed and then projecting beyond the dendrohyphidia"; DENDROHYPHIDIA 1-2 microns wide, richly branched, "covering the hymenium, visible to the naked eye as a white pruina"; HYPHAE monomitic, hyphae about 3 microns wide, colorless, thin-walled, with clamp connections, "densely interwoven in an interhyphal matrix", subiculum of varying thickness, thickest in the center of the fruitbody (often more than 0.1cm thick), (Eriksson)

Notes:
Peniophora polygonia has been found in BC, WA, ID, AB, MB, NF, NS, NT, ON, PQ, YT, AK, AZ, CO, MN, and NM, (Ginns). It has also been found in Europe including Switzerland (Breitenbach), and Denmark, Finland, Norway, and Sweden, (Eriksson).