Photograph of house eating fungs meruliporia Meruliporia incrassata - "Poria" the house eating fungus & Serpula lacrymans: infamous wood rotters
     


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This article describes Meruliporia incrassata or "Poria" Meruliporia incrassata, previously named Poria incrassata 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.

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What Meruliporia incrassata fungus or "Poria" the "house eating 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.

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.

Article Contents

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.

Why do Meruliporia or Serpula House-Eating Fungi Cause So Much Damage to Wood Structures?

Both Meruliporia incrassata and Serpula lacrymans [or lacrymans] are capable of causing very extensive damage to wood structures.

A particularly notorious wood-rotting species is Serpula lacrimans, which causes a condition commonly known as dry rot.

During the days of wooden ships, this fungus was a major cause of serious and widespread decay of sailing vessels (see Findley, 1982). In this regard, one James Sowerby (1752-1822) is said to have been the first consulting mycologist, having been hired by the [British] Royal Navy to reduce losses to decay in British warships.

Even today S. lacrimans is still important, primarily in Europe, where the dreaded dry rot causes tremendous damage to wooden structural elements and floors in houses and other buildings. The destructive effects are comparable to termite damage done to wooden structures in the United States. - Alexopolous et als. p6

In comprehending the ferocious ability of these wood-rotting fungi to attack buildings it is helpful to understand the powerful ability of these fungi to transport water rapidly and over distance. In fact the possibility of very long distances between their rhizomorphs and a distant mycelium front explains why when we find this fungus attacking a building we (and experts) recommend cutting back wood components six feet or more from any visible fungal infection.

We have already mentioned Serpula lacrimans and related wood species as dry rot fungi. The work of Thompson and her colleagues (1985) has shown that the velocity of water movement through rhizomorphs from the food source to the distant mycelium front may be as rapid as 475 cm per hour, depending upon external factors. It is furthermore interesting that in northern Europe the fungus is seldom collected outside of buildings. This is one species that appears to do well in the human-modified environment. - Alexopolous et als p588

Below right is shown some yellow fungus on wood wainscot which I suspected were more Meruliporia incrassata fruiting body material. But anotyher field photograph of mold growth shows (below left ) this fungus can also appear as dark brown on in areas of severe water damage - in this case on pine paneling.


Meruliporia incrassata in surprising places in a building (C) D Friedman

It was also a surprise to find Meruliporia among the brown crud showing at the base of this concrete block wall in another water-damaged building.

I believe that the wood subfloor beneath that vinyl sheet flooring was the host material for this mold colonization.

What Meruliporia incrassata mold spores look like under the microscope

Here is what Meruliporia incrassata spores look like in our lab. The spores in these lab photographs of Meruliporia incrassata were collected from buildings I inspected, including a surface sample found in a crawl space where they appeared as a "yellow dust" on rotting wood.

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

What is the Difference Between Meruliporia incrassata and Serpula lacrymans?

Serpula lacrymans has been mistaken in some articles as a European "synonym" for Merulius 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.

Serpula lacrymans and Meruliporia incrassata belong to different families (I use bold italics to indicate the official current names in these lists:

Meruliporia incrassata in air sample (C) D Friedman


Meruliporia incrassata
(Berk. & M.A. Curtis) Murrill, Mycologia 34(5): 596 (Murrill 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)

Our photo (left) illustrates Meruliporia found in an air sample collected during remediation of a mold and rot-damaged building.


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)

Serpula (Pers) Gray (1821), Coniophoracae. 2, widespread. S. lacrymans (syn. Merulius lacrymans), the dry rot or "house" fungus. See Cooke (1957: 201; key), Anon (Leafl. For.Prod. Res. Lab. 6, rev 1964), Harmsen (Friesia 6: 233, 1960; taxonomy, culture), Wood-attacking fungi. - Kirk et als.

Family Coniophoraceae. Members of Coniophoraceae are resupinate to pileate with a smooth or toothed hymenium. The hyphal construction of the context is usually mono or dimitic. Clamps may be present or not. However it is the basidiospores that are distinctive for the group.

The usually yellow to brown spores have smooth, doublewalls that take up cotton blue readily, the cyanophilous condition. In some species with large basidiospores it can be seen that only the inner wall is cyanophilous. Spores of some species also may be dextrinoid with Melzers reagent.

Another distinctive character is the brown rot produced by members of the family (Hallenberg, 1985). Based primarily on the basidiospore characters, this group long has been suggested as a relative of the boletes, and Ginns and Lefebvre (1993) placed the family in Boletales. - Alexopolous et als.

In sum, Merulius lacrymans (Boerhaave, 1720) is just one of many previous names or alternate names for what is now Serpula lacrymans (Accum,1827). 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 mycologist 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.

We 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.

In a New York home I found Meruliporia spores in settled dust under a kitchen sink. Later investigation discovered a long-standing leak into the building wall and extensive decay that had not been obvious from a simple visual inspection.

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 Press 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. Our 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.

 

Continue reading at MOLD CLEANUP GUIDE- HOW TO GET RID OF MOLD or select a topic from the More Reading links shown below.

Or see STRUCTURAL DAMAGE PROBING and see MOLD ON DIRT FLOORS - where we have also identified this fungus.

And to prevent building water entry or to fix a wet basement or crawl space, see our article series beginning at WATER ENTRY in BUILDINGS.

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