& Pouzar (1957) Mensularia ulmaria (Sowerby) Lázaro Ibiza, (1916) Microporus actinobolus (Mont.)

(1900) Rigidoporus ulmarius is a fungal plant pathogen found mainly on broad-leaved trees.

[1] The fruiting bodies are white, knobbly and relatively hard, requiring a fair amount of force to break.

[citation needed] Tubes are 1–5 mm long in each layer, pinkish to orange when young, browning with age, each layer separated by a thin contrasting band of white flesh.

Pores 5–8 per millimeter, red-orange fading to clay-pink or buff with age.

[citation needed] A fruit body of R. ulmarius discovered in Kew Gardens of London in 2003 was, for a time, the largest known fungal fruit body ever discovered, measuring 150 by 133 centimetres (59 by 52 in) in diameter, and had a circumference of 425 centimetres (167 in).

However, in 2011, a specimen of Phellinus ellipsoideus (formerly Fomitiporia ellipsoidea) significantly larger was discovered in China.