A Missing Mushroom Reappears After 125 Years: Resupinatus dealbatus

I spend a lot of time looking for fungi. Most of the time, my primary goal is to find species I've never found before. There are bucket-list ones, of course. For instance, I really want to find Galiella rufa – though, in that case, it's mostly so I can yell, "Peanut Butter Cup!" really loud in the woods. But what's even more fun is finding things that I've not only never found before, but ones that I also had no idea even existed before. These are the real treasures of my treasure hunts.

Galiella rufa, the Peanut Butter Cup, or Rubber
Fungus (Dan Molter, Mushroom Observer)

Years ago, when – for a while – I thought I knew a lot about mushrooms, whenever I found something I couldn't put a name on – even after hours of keying out in books and searching the internet – I would giddily leap to the conclusion that I'd found something very rare. Or maybe even – be still my heart! – something so rare it was new to science! 

I'm a calmer collector now. Having been humbled so many times by my own ignorance, I now know that the more I know, the more I know how very little I know. But I am getting better at accurately qualifying a never-seen-before find as something special. Better enough that, these days, if I come in from the woods and tell my husband I've found something "good," he knows he'll probably be the one making dinner. 

Vernal pond

I first found this particular "good" mushroom about six years ago in the late summer. There were three of them attached to a fallen branch. The limb was lying in an area that's flooded for a month or more each spring with a very large vernal pond, water long gone. The branch was too old to identify, though surrounding trees were all hardwoods, primarily oak, maple and ash. 

Dehydrated 

All three mushrooms were small (less than 1 cm), gilled and totally dehydrated. The most striking thing about them was that they had glowing white caps, but their gills were nearly black. I took them home, but since I didn't have a microscope at the time, couldn't get a spore print, and couldn't remember ever having seen a picture of such a thing, I knew I wasn't going to get anywhere until I at least found fresh samples (or got a microscope).  

A year later I found another batch on the same fallen limb. They weren't the slightest bit white. They were perky little hoes with dark grey-brown caps and stems, and similarly coloured gills. Later, at home, I determined that their spores were colourless, appearing white en masse. 

This photo shows their fabulous growth pattern – from tiny stemmed goblets 
with no sign of gills to flaring, multi-gilled hoes (click to see bigger).

There are lots of mushrooms whose gills are very dark at maturity because they produce very dark spores. It's uncommon, though, for light-spored mushrooms to have dark gills. A couple of these dark-gilled, white-spored mushrooms are decomposers, like mine. One is a tricky Gymnopus (a genus with predominantly white, cream, or yellowish gills), Gymnopus alkalivirens, but, though it sometimes grows on well-rotted wood, its shape was not a match. 

When I found these, their dark gill colour tricked me into thinking
 they would have dark spores. A white spore print
 quickly led me to their name: Gymnopus alkalivirens.

Another white-spored genus that includes many dark-gilled species seemed a closer fit: Resupinatus. Resupinatus grow on wood, and can be fan-shaped, but they are stemless, or have a small "pseudostipe." 

Though the gills of common Resupinatus applicatus can
be pale or brown or almost black, its spore print is always white.

Could the stems of mine be called pseudostipes? Were its "stipes" simply extensions of their caps? Maybe. Their growth pattern was certainly unusual. But a quick image search on the internet for Resupinatus got me nothing that matched my mushroom's distinctive hoe-shape. I, however, did learn that Resupinatus sporocarps begin growth with a smooth hymenium (the spore bearing surface of a mushroom) that eventually folds itself into gills (or pores) that multiply as the mushroom matures. Most other gilled mushrooms produce all their gills at the earliest stage of their development, which simply get bigger, deeper and longer as they mature.

I sliced through one. It clearly had the gelatinous layer that one expects to find in a Resupinatus. But that layer is also expected in another, related, genus of saprophytes – Hohenbuehelia. I searched that genus and found one species, H. petaloides, that actually showed a sort of similar form to my much smaller guys, though nothing else about it matched. At this point, I realized I was pretty well stuck until I got a microscope. 

And then I found this low-res picture on the internet:

Hohenbuehelia unguicularis (Greg Thorn)

It had the following description: "RGT #870601/19 (dry when collected), on dead lower branches of Populus tremuloides, Clarke Lake, Algonquin Provincial Park, Ontario, CANADA. When fresh or rehydrated, the fruiting bodies are a dark reddish brown (to black), with a fine, pallid pruina. Lamellae are dark in both fresh and dried states. Photo June 1, 1987, copyright R.G. Thorn."

This description was a closer fit than anything else, but it still wasn't a match. I was stuck with calling my collections Hohenbuehelia/Resupinatus with a question mark. 

And then I finally got myself a nice microscope. 

Before I went looking for new fresh samples of my "good" mushroom to scope them, I came across a couple of other Hohenbuehelia species. I love Hohenbuehelia, partly because some are carnivorous trappers (another blog to write!), and partly because they feature something showy under the microscope – large crystal-tipped, sterile cells in the gills called "metuloid" cystidia. I also love saying the name Hoehenbuehlia out loud, a name that could just as easily be a Shangri-la kind of place as a mushroom. It's where I want to go when I die. 

Hohenbuehelia mastrucata has jelly-filled points
on its cap when it's young and fresh.

Hohenbuehelia mastrucata metuloid cystidia

I finally looked under the microscope at a slice of the tiny mushrooms I kept finding. I fully expected to find metuloid cystidia. There were none. So it wasn't a Hohenbuehelia of any kind. Sheesh. Back to square one. I researched Resupinatus again. New stuff had arrived on the internet since my last search, but not my guy.

Meanwhile, I had begun seriously foraging in dried-up vernal ponds, which I had once thought were fungal dead zones. They're not. Along with finding all kinds of other fabulous things, I also discovered that my mystery mushrooms were not only widespread, growing on decorticated logs and limbs in four separate dried up vernal ponds (all on the same 150-acre property), they also had a very long growing season. When conditions were good, they started appearing before the end of June and didn't stop until late summer. Each fruiting body was also long-lived, sometimes rehydrating from a desiccated state none the worse for wear, and old sporocarps could persist through the winter. Colonies of bone-dry white ones stuck out like a sore thumb. Somebody had to have found these mushrooms before. How could I not find a name for it??

A log can look like this for two months

Their colour varies quite a bit – and sometimes has a purplish cast. 

I tried scoping it again, cutting at different angles to see if I was just missing the fancy cystidia. I still didn't find any. But I did find something else – strange many-pronged "jacks" on the cuticle of its cap. Image searches of variations on this description still didn't deliver my mushroom, though I did see quite a few unpleasant pictures of misshapen, fungus-infected toenails. 

Pileipellus "jacks"

And then in May, 2015, guess what I found? Resupinatus unguicularis. I wasn't absolutely sure, though, since I could find no descriptions or images of its metuloid cystidia to compare to the ones I saw in abundance under the microscope. 

Resupinatus unguicularis is dark grey or grey-brown with very dark
gills when fresh, but when dry, its cap fades almost to white.

Metuloid cystitis of Hohenbuehelia unguicularis

Eventually I figured out that the R. G. Thorn, who took the picture of H. unguicularis near the top of this post, is Greg Thorn, a professor at Ontario's Western University. He also seemed to be the right guy to approach about Resupinatus and Hohenbuehelia (see References below). 

I try not to make it a habit to bother such experts with identification questions, but – having exhausted all my available options – I really wanted to know a) whether H. unguicularis was the correct name for the black-gilled Hohenbuehelia, and b) what my "good" mushroom was. So I emailed him, attaching a bunch of images of both.  

Almost immediately, I got a reply. My tentative I.D. of H. unguicularis was, indeed, correct for the first mushroom. 

And here's what he said about the other, the one I'd spent three years – off and on – trying to name: 

"The second is an OMG! mushroom – I am willing to bet that this is Resupinatus dealbatus (otherwise known as Asterotus dealbatus). The specific epithet [dealbatus] means “becoming white.” A confirming character (although the shape and colouration are a good match for nothing else) is the morphology of the “fur” on the cap and stipe. Individual hyphae should have finger-like branches rather like “jacks.” You’re right, there are no pleurocystidia. The species has not been collected in Canada since John Macoun found it near Aylmer Quebec in 1893, but I suspect it is overlooked"

My "good" mushroom had got a name...and a promotion!

References:

Here's a description of Resupinatus dealbatus (Asterotus dealbatus) in an excerpt from Flora Agaricina Neerlandica - 3, Edited By: C Bas, T.W. Kuyper, M.E. Noordeloos and E.C. Vellinga; Aa Balkema, 1993

And another, on page 38 of this pdf (as Asterotus dealbatus): Hesler, L.R., "Panus Panellus Tactella Asterotus Notebook 1" (2013). Dr. Hesler Botanical Research.(Originally published March, 1958)

McDonald, J., 2015, Morphological and Molecular Systematics of Resupinatus (Basidiomycota)
Western University, London, ON

Thorn, R.G. 1986. The "Pleurotus silvanus" complex. Mycotaxon. 25(1):27-66.

Thorn, R.G.; Barron, G.L. 1986. Nematoctonus and the tribe Resupinateae in Ontario, Canada. Mycotaxon. 25(2):321-453

Read about Hohenbuehelia on Tom Volk's page (here) that includes notes on Ludwig Samuel Joseph David Alexander von Hohenbühel Heufler, thanks to Richard Aaron