Ascomycetes Wannabes: Cyphelloid Fungi—Part I

A few days ago I found a pale resupinate fungus growing on the side of a very rotten, mossy log up near Algonquin Park. Log-clinging fungi can be difficult to identify. There are a lot of them, and, outwardly, the majority are not particularly exciting. I took out my loupe to see if this one had anything fun going on—teeth, for instance, or velveteen bumps, or rubbery undulating ridges. I got something better, so much better that I actually did a double take: crowded on a cream-coloured cottony blanket were thousands of itsy-bitsy cups. Cups!

Porotheleum fimbriatum can produce thousands
 of tiny cups on a cottony subiculum. Click to see large.

Now, here's the thing—cup-shaped fungi are almost always ascomycetes that produce ejectable spores in asci. They can be big or tiny, hairy or smooth. They can be bright coloured or dull, stemmed or completely sessile. They can grow singly or scattered or in large clans. What they don't usually do is grow from an easy-to-peel-off cottony blanket half a metre long. 

Parts of the soft fruiting body of P. fimbriatum had engulfed mosses.

What I'd found was not an asco, but a peculiar basidiomycete called Porotheleum fimbriatum (also Porothelium fimbriatum or Stromatoscypha fimbriata).

The cups of P. fimbriatum are only 0.1-0.2 mm wide. They
can eventually become so crowded they resemble pores.

Porotheleum fimbriatum belongs to small group of cup-, disc-, or tube-shaped basidiomycetes that were once all lumped together in the genus Cyphella. By the end of the nineteenth century, however, enough differences had been noted between these tiny guys that most of the 300 described species had already been divvied up into a number of new genera.  

Cup-shaped cyphelloid fungi include Merismodes species.

It has long been proposed that these cyphelloid cups and tubes are "reduced forms" of much more "mushroomy" fungi. Evolution does not insist on making things ever more complex; sometimes an evolutionary trend is towards simplification. Many flowers that first evolved to form complicated collections of stamens and pistils have since progressed into simplified, or "reduced forms," in some cases paring down their reproductive organs to such an extent that they produce only a single stamen per male flower and a single pistil per female, a much more efficient use of a plant's resources. 

Examples of reduced-form evolution among vertebrates include animals whose ancestors had four limbs, but that are now either missing hind limbs or have no limbs at all, such as manatees, whales, snakes, and a few lizards.  

Anguis fragilis, a legless lizard (Lameiro)

In the case of reduced-form cyphelloid fungi, DNA sequencing shows some eye-opening connections with other species. Take, for instance, my strange fungal find P. fimbriatum. Molecular studies demonstrate that one of its very close siblings is Hydropus fuliginarius (Moncalvo et al, 2002). Other than H. fuliginarius's characteristic of producing a blackening latex, this rare little guy looks just like a normal mushroom, with cap and stem and gills. Who would have guessed it could have such an unlikely sister? Without sequencing, the only similarity between the two is that they're both saprophytes, obtaining their energy from rotting trees. 

Hydropus fuliginarius (Renée Lebeuf)

I've found other cyphelloid fungi—and almost every one has looked so much like an ascomycetes cup that I've been tricked into flipping first through my asco books before a lightbulb has gone off, sending me to where I should have been looking in the first place, in my basidiomycetes references. I'll deal with a few more of these curiosities in a couple of weeks, including one that has an even weirder sibling than P. fimbriatum.

References:

Porotheleum fimbriatum, CBS—KNAW Fungal Diversity Centre

Cyphelloid fungi

Hydropus fuliginarius, Mycoquebec

P. Bodensteiner et al. (2004). Phylogenetic relationships of cyphelloid homobasidiomycetes. Molecular Phylogenetics and Evolution 33(2):501-15.

Moncalvo, J. M., et al. (2002). One hundred and seventeen clades of euagarics. Molecular Phylogenetics and Evolution 23: 357–400
Peter Werner, 2004. Fungal Taxonomy III: The Euagarics. Mycena News.
Dick Rauh. Reduction and Fusion - Flowering Evolution. The Botanical Artist, Volume 13, Issue 1.