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The Genus Hypomyces  

by Michael Kuo, 1 October 2023

The species in Hypomyces are fungi that parasitize mushrooms, spreading over their surfaces as powdery tissues and pimply crusts. Often the parasite fungus so transforms its mushroom victim that it becomes hard to tell what the "host" was. (I just have to put "host" in quotation marks, even though that's the term used in mycology; hosting a Hypomyces is like asking the neighbors over for dinner and discovering that you're on the menu instead of those little sweet and sour meatballs you made.)

Generally speaking there are two stages—asexual and sexual—in the life of a Hypomyces. At first the fungus is asexual, and reproduces itself by cloning; with maturity the fungus becomes sexual and actual sexual reproduction occurs. These stages are sometimes called "imperfect" and "perfect" states (I bet you can guess which is which), or anamorphic and teleomorphic stages. Many Hypomyces species in the cloning, asexual stage were given scientific names and described in other genera (Cladobotryum, Mycogone, Sepedonium, Verticillium, and others), but current taxonomic rules mandate the use of the genus name representing the sexual stage.

Some Hypomyces species (for example the species that attack boletes) are rarely encountered in the sexual stage, while others are rarely found in the asexual stage—and there are plenty of Hypomyces species, in fact, for which the anamorph, or cloning stage, is not known. Thus identification of Hypomyces species does not always rely on consistent features, since cloning-stage fungi and sexual fungi are very different.

The key below treats 35 species of Hypomyces that might be expected in North America, and relies on identifying their victims with varying degrees of specificity, along with both macroscopic and microscopic features. For microscopic features I have used three terms that may be unfamiliar to those used to simply looking at "spores":

Ascospores are sexual-stage spores that have been produced in asci. This means they will only be found if you are examining a specimen in the sexual stage. Since species of Hypomyces are "pyrenomycetes," this means that tell-tale perithecia will be visible, to the naked eye or at least with the help of a hand lens.

Conidia are asexual spores that have been produced on hyphal structures called "conidiophores," most of which (in Hypomyces) look like skinny antlers or candelabras with prongs; the conidia form at the ends of the prongs by dividing themselves off: plop, plop, plop. In Hypomyces the conidia are generally smooth, and ellipsoid to cylindric.

Aleuriospores are conidia that have been formed differently; the Dictionary of the Fungi says aleuriospores are "developed from the blown-out end" of a conidiophore, "from which it secedes with difficulty." So, BLAM instead of plop, plop, plop. (Incidentally, the Dictionary also tells us the term "aleuriospore" is "obsol.," but I will continue to use it in this context since Hypomyces literature uses it.)

Some of the species in the key are not always as victim-specific as I have portrayed them. Hypomyces aurantius and Hypomyces tremellicola, especially, have been documented on a wide variety of mushrooms (including jelly fungi, chanterelles and trumpets, and others)—and in the case of Hypomyces aurantius, non-mushroom substrates (wood, soil) are sometimes documented. Additionally it should be noted that most of the species concepts in Hypomyces pre-date contemporary, DNA-based research; cryptic phylogenetic species have already been discovered (e.g. Nguyen et al. 2013) and more should be expected . . . possibly making the last month of my life (the time I spent revising my Hypomyces species pages and writing the key below) a waste of everyone's time. It's a good thing I'm retired, lol.


Hypomyces hyalinus
Hypomyces hyalinus

Hypomyces lactifluorum
Hypomyces lactifluorum

Hypomyces microspermus
Hypomyces microspermus

Hypomyces cervinigenus
Aleuriospores of Hypomyces cervinigenus

Key to 35 Species of Hypomyces in North America  

1.Victim a gilled mushroom.

1.Victim a mushroom without gills.

2.Victim pleurotoid (without a stem)—generally a species of Crepidotus or Pleurotus.
Hypomyces tremellicola

2.Victim with a well-defined stem.

3.Victim a species of Tubaria (usually Tubaria furfuracea).
Hypomyces tubariicola

3.Victim not a species of Tubaria.

4.Victim a species of Entoloma.
Hypomyces porphyreus

4.Victim not a species of Entoloma.

5.Victim a species of Pholiota.
Hypomyces succineus

5.Victim not a species of Pholiota.

6.Victim a species of Amanita (often Amanita rubescens).

6.Victim in the Russulaceae—a species of Russula, Lactarius, or Lactifluus.

7.Parasite brightly colored (orange, chrome yellow, yellow-green) when fresh.

7.Parasite white to pinkish, dull yellowish, or brownish to brown when fresh.

8.Parasite orange to yellow-orange (often becoming purple-orange to purple-red with old age), covering the entire victim; victim usually a large, white species (especially Russula brevipes, Lactarius deceptivus, and other species in the Lactarius piperatus group).

8.Parasite yellow to greenish yellow or bright green (duller green in old age), usually covering only the gills and stem.

9.Victim a species in the Lactarius camphoratus group; parasite lemon yellow, fading to whitish.
Hypomyces camphorati

9.Victim a species of Russula (usually a red- or purple-capped species); parasite yellow green, darkening to brownish olive.

10.Victim a Lactarius species in the Deliciosi section (milky caps with milk that is colored as exuded, and surfaces that often discolor dark green with age; see couplets 15–27 in the Lactarius key); ascospores under 20 µm long, not septate.

10.Victim, if a Lactarius, not in the Deliciosi section; ascospores varying in length, septate or not.

11.Victim in the Lactarius pubescens / Lactarius torminosus species group (birch-associated milky caps with pinkish to orange colors and woolly cap margins); parasite cream colored to brownish, with brown perithecia.
Hypomyces spadiceus
= lithuanicus, torminosus

11.Victim not usually in the pubescens / torminosus group; parasite whitish, with whitish to yellowish perithecia.

12.Mature ascospores septate once.
Hypomyces macrosporus

12.Mature ascopores not septate.
Hypomyces banningiae

13.Victim an ascomycete in Geoglossum, Helvella, Humaria, Leotia, or Trichoglossum (small club-shaped fungi, cup fungi, elfin saddles).

13.Victim not an ascomycete.

14.Victim a species of Geoglossum or Trichoglossum (small, club-shaped, mostly black fungi; see Geoglossum umbratile).
Hypomyces papulasporae

14.Victim not a Geoglossum or Trichoglossum.

15.Victim Humaria hemisphaerica (a small, pale cup fungus with tiny brown "eyelashes").
Hypomyces stephanomatis

15.Victim not Humaria hemisphaerica.

16.Victim a species of Leotia (small, rubbery, green and/or yellow club fungi; see Leotia viscosa).
Hypomyces leotiicola

16.Victim a species of Helvella ("elfin saddles" with irregular or cup-shaped caps, brittle flesh, and often-hollow stems).

17.Victim a bolete.

17.Victim a polypore or crust fungus.

18.Victim a species of Suillus.

18.Victim not a species of Suillus.

19.Parasite yellowish to brick red; victim Suillus acidus, or possibly other species of Suillus.
Hypomyces transformans

19.Parasite white becoming brownish to brown; victim Suillus spraguei.
Hypomyces completus

20.Victim Tylopilus rubrobrunneus or possibly another species of Tylopilus; parasite white when fresh, ascospores not septate.
Hypomyces melanocarpus

20.Victim not a Tylopilus; parasite color varying; ascospores septate once.

21.Parasite white at first, becoming brown without a yellow stage; aleuriospores yellow-brown in KOH, 25–30+ µm across; most ascospores under 15 µm long.
Hypomyces boletiphagus

21.Parasite white then pale yellow to golden before becoming brown; aleuriospores yellow to golden in KOH; aleuriospores and ascospores variously sized.

22.Victim xerocomelloid (small or medium-small boletes with slender stems and red to brown, dry, subvelvety caps that often become cracked and mosaic-like; see Xerocomellus chrysenteron, Xerocomellus rubellus, and Boletus harrisonii for examples); aleuriospores round, 12–15 µm across.

22.Victim xerocomelloid or not; aleuriospores round or not, variously sized.

23.Parasite usually white, then pale yellow, then brown; aleuriospores elongated and ridged (appearing a bit like dried prunes).
Hypomyces chlorigenus

23.Parasite usually white, then pale yellow, then dark yellow to golden yellow, then brown; aleuriospores round and spiny, 15–25 µm across.

24.Victim a crust fungus.

24.Victim a polypore.

25.Victim a species of Stereum (see Stereum ostrea for a representative).
Hypomyces sympodiophorus

25.Victim Xylobolus frustulatus or another species of Xylobolus.
Hypomyces xylobolus

26.Victim Trametes versicolor or another species of Trametes.

26.Victim not usually a species of Trametes.

27.Parasite white to pink, peach, or yellow; conidia 14–19 x 8–10 µm; ascospores 17–23 x 5–6.5 µm.
Hypomyces mycophilus

27.Parasite white to buff or tan; conidia 18–28 x 6–8 µm; ascospores 15–20 x 3–4 µm.
Hypomyces polyporinus

28.Parasite white to buff or pale tan–not becoming more highly colored.

28.Parasite, if white to buff at first, becoming more highly colored: orange, pink to red, pale to deep yellow, or green.

29.Ascospores smooth, under 20 µm long; conidia cylindric (11–20 x 2–4 µm).
Hypomyces chrysostomus

29.Ascospores verrucose, more than 20 µm long; conidia ellipsoid, variously sized.

30.Ascospores 19–24 µm long, septate once; conidia 12–24 µm long, septate once.
Hypomyces orthosporus

30.Ascospores 30–35 20 µm long; conidia 17–46 µm long, septate twice.
Hypomyces tegillum

31.Parasite becoming green or developing green spots as the conidia are developed.
Hypomyces viridigriseus

31.Parasite not developing green colors.

32.Parasite becoming pink to red.
Hypomyces rosellus

32.Parasite becoming yellow to orange.

33.Parasite usually bright orange; perithecia orange-red, turning purple in KOH.
Hypomyces aurantius

33.Parasite becoming pale to dark yellow; perithecia amber to orange, purple or negative with KOH.

34.Perithecia purple with KOH; ascospores 14–16 µm long.
Hypomyces subiculosus

34.Perithecia negative with KOH; ascospores 19–23 µm long.
Hypomyces semitranslucens


Das, K. & D. Chakraborty (2013). New record of parasitic macrofungus from India. Indian Journal of Plant Sciences 2: 73–75.

Douhan, G. W. & D. M. Rizzo (2003). Host-parasite relationships among bolete infecting Hypomyces species. Mycological Research 107: 1342–1349.

Harrison, K. A. & Grund, D. W. (1977). Nova Scotian fleshy fungi: A new albino variant of Hypomyces lactifluorum (Schw. Ex Fr.) Tulasne. Proceedings of the Nova Scotian Institute of Science 28: 87–91.

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Laperriere, G., I. Desgagné-Penix & H. Germain (2018). DNA distribution pattern and metabolite profile of wild edible lobster mushroom (Hypomyces lactifluorum/Russula brevipes). Genome 61: 329–336.

Lechat, C., A. Gardiennet & J. Fournier (2017). First report of a lichenicolous species of Hypomyces (Hypocreaceae), H. peltigericola sp. nov. 9: 23–26.

Parker, A. D. (1990). Noteworthy species of Hypocrea, Hypomyces, and Thuemenella (Ascomycetes, Hypocreales) from Wisconsin. Mycotaxon 38: 77–82.

Põldmaa, K. (1996). A new species of Hypomyces and three of Cladobotryum from Estonia. Mycotaxon 59: 389–405.

Põldmaa, K., G. J. Samuels & D. J. Lodge (1997). Three new polyporicolous species of Hypomyces and their Cladobotryum anamorphs. Sydowia 49: 80–93.

Põldmaa, K. (1999). The genus Hypomyces (Hypocreales, Ascomycota) and allied fungicolous fungi in Estonia. I. Species growing on aphyllophoralean basidiomycetes. Folia Cryptogamica Estonica 34: 15–31.

Põldmaa, K., E. Larsson & U. Kõljalg (1999). Phylogenetic relationships in Hypomyces and allied genera, with emphasis on species growing on wood-decaying homobasidiomycetes. Canadian Journal of Botany 77: 1756–1768.

Põldmaa, K. & G. J. Samuels (1999). Aphyllophoricolous species of Hypomyces with KOH-negative perithecia. Mycologia 91: 177–199.

Põldmaa, K. (2000). Generic delimitation of the fungicolous Hypocreaceae. Studies in Mycology 45: 83–94.

Põldmaa, K. (2003). Three species of Hypomyces growing on basidiomata of Stereaceae. Mycologia 95: 921–933.

Põldmaa, K. (2011). Tropical species of Cladobotryum and Hypomyces producing red pigments. Studies in Mycology 68: 1–34.

Rogerson, C. T. & Simms, H. R. (1971). A new species of Hypomyces on Helvella. Mycologia 63: 416–421.

Rogerson, C. T. & G. J. Samuels (1985). Species of Hypomyces and Nectria occurring on Discomycetes. Mycologia 77: 763–783.

Rogerson, C. T. & G. J. Samuels (1989). Boleticolous species of Hypomyces. Mycologia 81: 413–432.

Rogerson, C. T. & G. J. Samuels (1993). Polyporicolous species of Hypomyces. Mycologia 85: 231–272.

Rogerson, C. T. & Samuels, G. J. (1994). Agaricolous species of Hypomyces. Mycologia 86: 839–866.

Rossman, A. Y. & 15 coauthors (2013). Genera in Bionectriaceae, Hypocreaceae, and Nectriaceae (Hypocreales) proposed for acceptance or rejection. IMA Fungus 4: 41–51.

Valdez, G. U. & G. W. Douhan (2012). Geographic structure of a bolete-infecting cryptic species within the Hypomyces microspermus species complex in California. Mycologia 104: 14–21.

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