Differs from other Haploporus species by the combination of a resupinate habit, a dimitic hyphal structure with non-dextrinoid skeletal hyphae, the presence of ventricose cystidioles occasionally with a simple septum, dissepimental hyphae usually with a simple septum, unique thick-walled basidia and distinct wide oblong basidiospores measuring 13.5–16.5 × 7.5–9.5 µm.

CHINA. Yunnan Prov., Xinping County, Ailaoshan Nat. Res., on rotten angiosperm wood, 15 Oct. 2013, Dai 13580 (Holotype in BJFC).

Crassus (Lat.): referring to the species having wide basidiospores.

Basidiocarps annual, resupinate, adnate, soft corky when fresh, become corky and cracked upon drying, without odor or taste when fresh, up to 35 cm long, 3 cm wide and 1 mm thick at center. Pore surface white to cream when fresh, becoming buff-yellow upon drying; sterile margin indistinct, very narrow to almost lacking; pores round, 3–5 per mm; dissepiments thin, mostly entire, sometimes lacerate. Subiculum cream, corky, thin, about 0.1 mm thick. Tubes light buff, corky, about 0.9 mm long.

Hyphal system dimitic: generative hyphae bearing clamp connections, hyaline, thin-walled; skeletal hyphae dominant, thick-walled, frequently branched, IKI–, CB+, tissues unchanging in KOH.

Generative hyphae infrequent hyaline, thin-walled, rarely branched, 1.5–2.5 µm in diam; skeletal hyphae dominant, hyaline, thick-walled with a narrow lumen, frequently branched, interwoven, 1–2 µm in diam.

Generative hyphae frequent, hyaline, thin-walled, occasionally branched, 1.5–3 µm in diam; skeletal hyphae dominant, distinctly thick-walled with a narrow to wide lumen, frequently branched, interwoven, 1.5–2.5 µm in diam; dissepimental hyphae usually with a simple septum. Cystidia absent; cystidioles present, ventricose, usually with a small umbo having a simple septum, occasionally with a few small guttules, 21–31× 8–10 µm. Basidioles thick-walled, dominant, similar in shape to basidia, but smaller; basidia thick-walled, pear-shaped to barrel-shaped with 4-sterigmata and a basal clamp connection, occasionally with some small guttules, 22–31 × 8–13 µm; dendrohyphidia absent. Some irregular-shaped crystals present among tube tramal stru ctures.

Basidiospores oblong, hyaline, thick-walled, with tuberculate ornamentation, IKI–, CB+, 13.5–16.5(–17) × (7–)7.5–9.5 µm, L = 15.06 µm, W = 8.15 µm, Q = 1.85 (n = 30/1).