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• Meruliporia incrassata - "Poria" the house eating fungus
• Photographs of Meruliporia incrassata in buildings and under the microscope
• What to do about Meruliporia incrassata when it is found in a building

Meruliporia incrassata, previously named Poria incrassala which is better known among reporters and repairmen who like to see the public pale as the "house eating fungus. This is a severe wood-rot fungus (a basidiomycete) which is particularly onerous in buildings because, as some writers have claimed, it may to continue to find water for itself even after the original wet-building leaks appear to have been repaired. To obtain its moisture, this fungus has been observed to extend long rhizomorphs through wood structural and non-structural members, both inside the wood and even on other surfaces. It is capable of extending its water supply pumping rhizomorphs over considerable distances to find a needed moisture source. That's why the repair advice is to remove 24 inches or more of wood BEYOND any visible damage and rot. Otherwise you're not getting rid of all of the infected material, and the fungus may re-grow quickly. Not all mycologists agree with this characterization of Meruliporia incrassata, as I elaborate below. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

What Meruliporia incrassata fungus looks like in a building

Here is an example of Meruliporia in an old building. This was an old schoolhouse with an inaccessible wet crawl. The center girder was completely destroyed by this wood rotting fungus. Here are some Meruliporia rhizomorphs suspended under wood flooring and some yellow fungus on wood wainscot which I suspected were more Meruliporia incrassata fruiting body material.

What Meruliporia incrassata mold spores look like under the microscope

Here is what Meruliporia incrassata spores look like in my lab. These were spores collected from a surface sample found in a crawl space where they appeared as a “yellow dust” on rotting wood.

Meruliporia incrassata, Merulius lacrymans, Serpula lacrymans,- Getting the Fungal Names Right

Serpula lacrymans has been mistaken in some articles as a European "synonym" for Merilus lacrymans which I used to characterize as Meruliporia. before Mr. Green was kind enough to set me straight by generously informing me (email in September 2006) that Serpula lacrymans and Meruliporia incrassata are completely different species of fungus. They belong to different families (I use bold italics to indicate the official current names in these lists:

Meruliporia incrassata (Berk. & M.A. Curtis) Murrill, Mycologia 34(5): 596 (1942) - http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=288330
where some synonyms are listed going back to 1849:
Merulius incrassatus Berk. & M.A. Curtis, Hooker's J. Bot. 1: 234 (1849)
Poria incrassata (Berk. & M.A. Curtis) Burt, Ann. Mo. bot. Gdn 4: 360 (1917)
Serpula incrassata (Berk. & M.A. Curtis) Donk, Bulletin du Jardin Botanique de Buitenzorg, 3 S™rie 17(4): 474 (1948)
Sesia incrassata (Berk. & M.A. Curtis) Kuntze, Revis. gen. pl. (Leipzig) 2: 870 (1891)
while
Serpula lacrymans (Wulfen) J. Schr™t., Meddn Soc. Fauna Flora fenn. 11: 21 (1885) - http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=102458
has a still longer list of synonyms:
Boletus lacrymans Wulfen, in Jacquin, Misc. Austriaca 2: 111 (1781)
Boletus obliquus Bolton, Hist. fung. Halifax: tab. 74 (1788)
Gyrophana lacrymans (Wulfen) Pat., Essai Tax. Hym™nomyc. 39(2): 108 (1900)
Merulius destruens Pers., Syn. meth. fung. (G™ttingen): 496 (1801)
Merulius domesticus H.G. Falk, Hausschwammforsch. 6: 53 (1912)
Merulius giganteus Saut., Hedwigia 16: 72 (1877)
Merulius guillemotii Boud. [as 'guillemoti'], Bull. Soc. mycol. Fr. 10(1): 63 (1894)
Merulius lacrymans (Wulfen) Schumach., Enum. pl. (Kjbenhavn) 1: 371 (1801)
Merulius lacrymans var. guillemotii (Boud.) Boud., Icon. mycol., S™r. 1 4: 84 (1905)
Merulius lacrymans var. terrestris Peck, Ann. Rep. N. Y. state Mus. 49: 45 (1897)
Merulius terrestris (Peck) Burt, Ann. Mo. bot. Gdn 4: 346 (1917)
Merulius vastator Tode, Abh. naturforsch. Ges. Halle 1: 351 (1783)
Serpula destruens (Pers.) Gray, Nat. Arr. Brit. Pl. (London) 1: 637 (1821)
Serpula domestica (Falck) Bondartsev, Priroda: 41 (1948)
Serpula terrestris (Burt) S. Ahmad, Monogr. Biol. Soc. Pakistan 6: 29 (1972)
Sesia gigantea (Saut.) Kuntze, Revis. gen. pl. (Leipzig) 2: 870 (1891)
Sistotrema cellare Pers., Syn. meth. fung. (G™ttingen): 554 (1801)

In sum, Merulius lacrymans is just one of many previous names or alternate names for what is now Serpula lacrymans. Serpula lacrymans is the current name for that fungus. Note the spelling difference too.

Indeed this is part of the fun of mycology. When mycologists take a break from the field and lab to get together, each time they do the result is a whole lot of shifting around, reclassifying of fungi, and changing of some of them to better or newer names. This process is bound to accelerate as more sophisticated methods for classifying fungi are put to use, such as DNA analysis. The traditional visual bases for taxonomic decisions about what to call things and what families to put them into is being upset and we've discovered that just because two organisms share a lot of features one cannot assume they are close relatives or members of the same family. It was easier in the old days when Talbot's Fungal Taxonomy explained family membership based almost entirely on physical appearance and attributes. But then, he didn't have the tool of DNA analysis.

Perhaps Serpula is more commonly identified in Europe and Meruliporia more commonly identified in the U.S. - I'm no longer sure that they don't both occur in both locales. As John Haines says, "all mold is everywhere, all the time." Readers who want to see building-damage-related articles which are often less scientifically rigorous may look up Meruliporia incrassata's reputation under "poria the house eating fungus" or "Meruliporia ..." where they will be deluged with scary articles from the real estate world (and from some home inspectors), wood preservation research, and some more scholarly articles from mycologists.

I prefer to use the Meruliporia incrassata name for this U.S. occurring brown-rot fungus. Just do a search on both names and you'll see what I mean.

More-accurate details about how Meruliporia incrassata causes rot and grows in buildings

This is actually a pretty common basidiomycete in older houses which have been exposed to leaks. I have found Meruliporia spores indoors in surface dust samples and (rarely) airborne (when there has been demolition or mold remediation ongoing). When I find these spores in a building I suspect a hidden but serious rot problem.

Matt Green, who didn't identify himself but sounds like a mycologist who knows Meruliporia incrassata has suggested some more carefully worded facts about this fungus which I quote or paraphrase here from email received in 2006.

Meruliporia's fungal transport of water

Fungal rhizomporphal strands do not convey water in exactly in the manner I described in the introduction, though I didn't make that version up myself. Green points out that the extended rhizomorphs sent out by Meruliporia incrassata reduce the exposed surface area of the hyphae, which in turn reduces water evaporation. This saves water, it doesn't move it. Sarah Watkinson goes into more detail in a forthcoming book Fungi in the Environment, Edited by Geoff Gadd, Sarah Watkinson and Paul Dyer, Series: BRITISH MYCOLOGICAL SOCIETY SYMPOSIA 25 364 pages, 42 line diags, 48 half-tones, 10 tabs., Cambridge University Pres which you will eventually be able to order at http://www.nhbs.com/title.php?tefno=147466

What to do about fungus-infected structural wood in buildings

Green added that as long as the timber is dry, no further decay is going to occur. You might get shrinkage once the timber dries, but that's not indicative of active decay. "Current thinking is that removing the source of water, allowing the building to dry and removing decayed timber is a more sustainable approach." He cites Timber Decay in Buildings: The Conservation Approach to Treatment, by Brian Ridout, John Fidler, Ingval Maxwell, ISBN: 0419188207, Spon Press, 1999, and available at http://www.buildingconservation.com/books/a46.htm if you're in the UK or from Amazon.com (US $80 but available used for less). This is a good book which includes advice on obtaining wood rot resistance with less reliance on environmentally harmful chemicals.

The tricky part is "as long as the timber is dry" as Green penned in his note. My field experience suggests that over the 20-year life of a wood-frame building, basements and crawl spaces rarely stay dry except in arid climates where this wood rotting fungus won't be much of a problem in the first place. Indeed no amount of fungal excising is going to be sufficient to protect a building from rot down the road if wet conditions are recurrent. Readers might want to take a look at the articles we provide on how to prevent mold in buildings.

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More Information on Meruliporia incrassata, Wood Rot in Buildings, Environmental and Building Diagnostic Inspections and Repairs

• The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

• http://www.fpl.fs.fed.us/documnts/pdf1999/carll99a.pdf Decay of Wood and Wood-Based Products Above Ground in Buildings, Charles G. Carll and Terry L. Highley
• http://cecontracosta.ucdavis.edu/Wood_Durability/What_Causes_Gaps_Between_Boards-.htm U. California - Davis on wood rot
• http://www.treesearch.fs.fed.us/pubs/viewpub.jsp?index=6360 US Forest Products Research Lab
• http://www.fpl.fs.fed.us/research-areas/rwu/rwu4723/preservation_faqs/publications.html US Forest Products Research Lab Yang and Illman's research on fungicidal tolerance of Meruliporia
• http://www.cnr.berkeley.edu/forestry/extra.html U Cal Center for Forestry
• http://www.psms.org/sporepr/sp351.html
• http://botanika.bf.jcu.cz/mykologie/polypores/list_iton.html Czechoslovakian pix - you won't see it in a house looking like this however
• http://www.pruverani.com/sellersnews.asp?ID=1204 - a typical collapsing house case
• http://www.human.cornell.edu/units/dea/extension/docs/fal96/fungi.htm Cornell University resource on wood destroying fungi
• http://www.germology.com/rot.htm soft rot, white rot, brown rot distinguished
• http://alcor.concordia.ca/~raojw/crd/essay/essay000077.html

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