Summary:
Features include 1) resupinate growth on conifers and hardwoods, 2) fruitbodies that are waxy to crustaceous, circular at first but becoming confluent, colored whitish to grayish or less often yellowish, the surface membranaceous, often cracking into polygons, the margin abrupt, 3) spores that are nearly round to elliptic, smooth, inamyloid, and colorless, 4) dendrohyphidia that are sometimes difficult to find, 5) gloeocystidia with oily, homogeneous, yellow content or resinous content, and 6) a dimitic hyphal system, the generative hyphae with clamp connections. The online Species Fungorum, accessed September 8, 2012 gave the current name of this subspecies as Cystostereum pini-canadense (Schwein.) Parmasto (and note that Eriksson(3) had used the name Cystostereum subabruptum for Crustomyces pini-canadensis subsp. subabruptus).

Microscopic:
SPORES 3-5(7) x 2-3(4) microns, nearly round to elliptic, slightly curved or flattened adaxially, smooth, inamyloid, colorless, thin-walled, uninucleate, ballistosporic; BASIDIA 4-spored, 12-20 x 4-5 microns, narrowly clavate to short-cylindric, "often bent at an obtuse angle, sometimes with a median constriction", with basal clamp connection; DENDROHYPHIDIA "present in hymenium, sometimes difficult to find", tapering to 1 micron wide, "thin-walled, sometimes encrusted"; gloeocystidioid vesicles 10-30 x 6-15 microns, abundant in hymenium, few in subiculum, subglobose, pyriform to clavate, "mostly terminal but occasionally intercalary modifications of generative hyphae, when terminal with a basal clamp, often possessing up to 3 apical moniliform bulbs", with oily, homogeneous, yellow content or a resinous content that shrinks and finally dissolves within 10 minutes in 3% KOH, negative in sulfoaldehydes; HYPHAE dimitic: 1) generative hyphae, 1-3(4) microns wide, thin-walled to thick-walled, colorless, nodose-septate [septa with clamp connections], 2) skeletal hyphae 1-2(3) microns wide, thick-walled, colorless, "abundant to rare in the basal layer, rare elsewhere, occasionally branched enough to be interpreted as binding hyphae", (Chamuris)

Notes:
Crustomyces pini-canadensis subsp. pini-canadensis has been found in BC, WA, OR, MB, NF, ON, PE, PQ, CA, MI, MN, MO, MT, NC, NH, NY, PA, WI, and WV, (Ginns).

Synonyms and Alternate Names:
Helotium sulfurinum Quel.