Irpex lacteus

Description

Irpex lacteus is a common crust fungus distributed throughout temperate areas of the world. It is the type of the genus Irpex. Irpex lacteus is considered a polypore, but depending on growth conditions it can also produce a hydnoid hymenophore. Due to this variability and abundance of the species, it has been described as a new species to science numerous times and subsequently has an extensive synonymy. The complete genome sequence of Irpex lacteus was reported in 2017.

The brackets often fuse to form long rows. The caps may be very small in comparison to the spreading, resupinate portions of this fungus. Compare to Xylodon paradoxus, a potential look-alike species.

Irpex lacteus is a white-rot fungus that inhabits mainly angiosperm branches and trunks. It is one of the most common wood-rotting fungi for instance in urban North America. It is inedible. The fungus has been identified as a cause of pulmonary infections in immunocompromised humans.

Mushroom Identification

1. Ecology

   Saprobic; spreading across the bottoms and sides of fallen hardwood logs (occasionally on the wood of conifers); annual; causing a white rot of the sapwood and rarely the heartwood; occasionally reported as parasitic on the living wood of cherry trees; appearing year-round; widely distributed in North America but rare or absent in the Southwest.

2. Fruiting Body

   A spreading patch of whitish pore surface with 2-3 pores per mm, soon becoming tooth-like rather than poroid, except near the margin; developing shelflike edges or even caps when growing on the sides of logs; caps when present kidney-shaped to irregular, with a whitish to grayish (often zoned), velvety to hairy upper surface; flesh thin, whitish, and tough; without a stem.

3. Chemical Reactions

   All parts are brownish orange with KOH.

4. Spore Print

   White.

5. Microscopic Features

   Spores 5-7 x 2-3 µ; smooth; elliptical to subcylindric; hyaline in KOH; inamyloid. Cystidia conspicuous; abundant to scattered; 50-110 x 5-10 µ; encrusted apically or over nearly the whole length. Thin-walled generative hyphae frequently branching; 2-4 µ wide. Thick-walled skeletal hyphae rarely branching; 2.5-6 µ wide. Clamp connections are absent.

Look-Alikes

Trichaptum is generally more pileate and less effused, and pores turn from violet to cream (not white). Xylodon (was = Schizopora) has generally shallower maze-like pores and no reflexed edges. Trametopsis cervina has reflexed caps that resemble a Trametes and the irregular pores are not deeply lacerate and split. Spongipellis pachyodon has larger caps and is less effused. Some Antrodia may get jagged pores but pores are usually not deeply lacerate and split. Steccherinum and other hydnoid species have rounded teeth or spines rather than flat jagged and split pores.

Synonyms

1. Boletus cinerascens Schwein. (1822)

2. Boletus tulipiferae Schwein. (1822)

3. Coriolus lacteus (Fr.) Pat. (1900)

4. Coriolus tulipiferae (Schwein.) Pat. (1900)

5. Daedalea diabolica Speg. (1889)

6. Hirschioporus lacteus (Fr.) Teng (1963)

7. Hydnum lacteum (Fr.) Fr. (1823)

8. Irpex bresadolae Schulzer (1885)

9. Irpex diabolicus (Speg.) Bres. (1919)

10. Irpex hirsutus Kalchbr. (1878)

11. Irpex lacteus f. sinuosus (Fr.) Nikol. (1953)

12. Irpex pallescens Fr. (1838)

13. Irpex sinuosus Fr. (1828)

14. Irpiciporus lacteus (Fr.) Murrill (1907)

15. Irpiciporus tulipiferae (Schwein.) Murrill (1905)

16. Microporus chartaceus (Berk. & M.A.Curtis) Kuntze, (1898)

17. Microporus cinerascens (Schwein.) Kuntze (1898)

18. Polyporus chartaceus Berk. & M.A.Curtis (1849)

19. Polyporus tulipiferae (Schwein.) Overh. [as 'tulipiferus'], (1915)

20. Polystictus bresadolae (Schulzer) Sacc. (1888)

21. Polystictus chartaceus (Berk. & M.A.Curtis) Cooke, (1886)

22. Polystictus cinerascens (Schwein.) Cooke (1886)

23. Polystictus cinerescens (Schwein.) Cooke

24. Polystictus tulipiferae (Schwein.) Cooke (1886)

25. Poria cincinnati Berk. ex Cooke, (1886)

26. Poria tulipiferae (Schwein.) Cooke, (1888)

27. Sistotrema lacteum Fr. (1818)

28. Steccherinum lacteum (Fr.) Krieglst. (1999)

29. Trametes lactea (Fr.) Pilát (1940)

30. Xylodon bresadolae (Schulzer) Kuntze (1898)

31. Xylodon hirsutus (Kalchbr.) Kuntze (1898)

32. Xylodon lacteus (Fr.) Kuntze (1898)

33. Xylodon pallescens (Fr.) Kuntze (1898)

34. Xylodon sinuosus (Fr.) Kuntze (1898)

Photo sources:

Photo 1 - Author: Liz Popich (Lizzie) (CC BY-SA 3.0)

Photo 2 - Author: Otto Miettinen (CC BY-SA 3.0)

Photo 3 - Author: Otto Miettinen (CC BY-SA 3.0)

Photo 4 - Author: Liz Popich (Lizzie) (CC BY-SA 3.0)