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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
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.
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.
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.
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
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.
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 (Berk. & M.A. Curtis) Murrill, Mycologia 34(5): 596 (Murrill 1942)
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.
Serpula lacrymans (Wulfen) J. Schr™t., Meddn Soc. Fauna Flora fenn. 11: 21 (1885) -
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
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.
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Bagchee K. (1954) Merulius lacrymans (Wulf.) Fr. in India. Sydowia 8: 80–85
White NA, Dehal-Prabhjyot K, Duncan JM. (2001) Molecular analysis of intraspecific variation between building and 'wild' isolates of Serpula lacrymans and their relatedness to S. himantioides. Mycological Research 105: 447–452.
Cooke WB. (1955). Fungi of Mount Shasta (1936–51). Sydowia 9: 94–215.
Harmsen L. (1960). Taxonomic and cultural studies on brown-spored species of the genus. Friesia 6: 233–277.
Kotlaba F. (1992). Nalezy drevomorky domaci — Serpula lacrymans v prirode. Ceska Mykologie 46: 143–147.
Kauserud H, Högberg N, Knudsen H, Elborne SA, Schumacher T. (2004). Molecular phylogenetics suggest a North American link between the anthropogenic dry rot fungus Serpula lacrymans and its wild relative S. himantioides. Molecular Ecology 13: 3137–3146.
Kauserud H, Svegården IB, Saetre GP, Knudsen H, Stensrud Ø, Schmidt O, Doi S, Sugiyama T, Högberg N (August 2007). "Asian origin and rapid global spread of the destructive dry rot fungus Serpula lacrymans". Mol. Ecol. 16 (16): 3350–60. doi:10.1111/j.1365-294X.2007.03387.x. PMID17688538.
Serpula Lacrymans Fundamental Biology and Control Strategies, edited by D.H. Jennings and A.F. Bravery, Wiley, West Sussex, 1991, ISBN 9780471930587. Quotes are from page 9 of the introduction in the book.
Olaf Schmidt (2006). Wood and Tree Fungi: Biology, Damage, Protection, and Use. Berlin: Springer. ISBN3-540-32138-1.
Atlas of Clinical Fungi, 2nd Ed., GS deHoog, J Guarro, J Gene, & MJ Figueras, Centraalbureau voor Schimmelcultures, Universitat Rovira I Virgili, 2000, ISBN 90-70351-43-9 (you can buy this book at Amazon) - The Atlas of Clinical Fungi is also available on CD ROM
Atlas of Indoor Mold, Online Clinical Mold Atlas, Toxins, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
"A Brief Guide to Mold, Moisture, and Your Home",
U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm