A Novel Way to Reproduce: Pleonectria strobi

Pleonectria strobi

Surprise! Something really small! I can't help it—it's still too early here for morels or any other macrofungi so I've been wandering through the snowless, leafless woods looking for out-of-place dots. White dots on branches could be Lachnellula, yellowy orange dots on rotting logs could be one of the smaller Dacrymyces, vivid blue-green ones could be just-starting Chlorociboria. You never know what you're going to find when you're looking for dots, and two days ago I found some some very interesting ones.

Pleonectria strobi can be up to 1 mm., but are usually smaller. 

They were minute and orange, growing in clusters along the length of a twig. I thought at first they were tiny cups, but on closer inspection saw that they were actually some kind of Nectria that had become cupulate from drying in the sun. Moistened, they became much more globose. But what kind? Nectria cinnabarina, which is relatively common, is restricted to broadleaf trees. The ones I'd found, though, had erupted from pine—specifically white pine (Pinus strobus). They also seemed smaller than Nectria cinnabarina and brighter orange, the brightness due to a yellow scurfiness on their surface.  

To get a clearer idea of what they were, I squashed a few under a slide cover and stuck then under the microscope. I immediately found multiple asci, most of which were jam-packed with very tiny, slightly curved spores, so packed that, even as I watched, they were bursting out in streams of a hundred at a time. Very exciting, but also very wrong. Nectria species are supposed to produce asci containing 8 ascospores apiece, not hundreds. So what was up?

Ascoconidia streaming out of ascus.

It turns out that what I was seeing were not ascospores but ascoconidia, and what I'd found was not a simple Nectria, but a Pleonectria.

Asci stuffed with ascoconidia.

Many ascomyctes have two different ways of reproducing: sexually and asexually. Asexually they produce conidiophores that release conidiospores, which are haploid, having only one set of chromosomes instead of two. I've seen lots of conidiospores before, but none of them had been inside asci. That's because asci, as a rule, are normally reserved for the production of ascospores. This is not, however, the case for some rule-breaking Pleonectria, including the one I had found, Pleonectria strobi. As is to be expected, each Pleonectria strobi ascus first produces 8 ascospores, but then the fun starts. Ascoconidia bud off each of the filiform, multiseptate ascospores, so many, in fact that, according to Fungi of Switzerland, Vol.1, the ascospores are completely consumed. 

The multiseptate ascospores of Pleonectria strobi
look a little wormlike and vary in length.

The ascospores were certainly extremely difficult to find under the microscope. Interestingly, the ones I eventually did find were outside the asci, so perhaps not all of them are doomed to the service of generating ascoconidia. 

Reference:

Hirooka Y, Rossman AY, Samuels GJ, Lechat C, Chaverri P. (2012) A monograph of Allantonectria, Nectria, and Pleonectria (Nectriaceae, Hypocreales, Ascomycota) and their pycndial, sporodochial, and synnematous anamorphs. Studies in Mycology 71: 1–210.

With a Little Help from Arthropods: Catinella olivacea

Fresh Catinella olivacea (photo courtesy Andreas Gminder)

By March the snow that had accumulated since November was so deep in the woods that my search for winter fungi was mostly confined to standing trees and hung logs. I found the shrivelled little black discs (below) on the underside of a dead alder suspended above the snow. 

Shrivelled Catinella olivacea in winter.

Though they looked quite degraded, I managed to perk them up enough at home with warmth and a bit of moisture to not only get a vague idea of their truer form, but to also get a spore sample. 

The slipper-shaped spores of Catinella olivacea.

The ascospores are pretty cute—they look just like those outlines of feet, both men's and women's, that they used to use in diagrams to show dance steps. These foot-shaped ascospores helped me figure out that what I'd found was Catinella olivacea (or Karschia olivacea in older books). 

My 25-cent lawn-sale Rhumba lesson record.
See? Catinella spores.

They're small disc-shaped fungi, even when fresh (2-15 mm diam.), and attractively bicoloured, with a greenish- to olive-black fertile surface rimmed with a slightly raised, paler, ochreous margin. The fertile surface is often studded with beads of moisture.

Catinella olivacea is an ascomycete that's not uncommon, just rarely found since its usual haunts are either deep inside rotting cavities or hiding on the undersides of logs. Most fungi rely on air currents to disperse their spores. Not Catinella olivacea. Tucked away and sheltered from wind, it has evolved another strategy to move its spores around. The fertile surface becomes gelatinous at maturity, trapping the forcibly ejected ascospores in sticky droplets. All this fungi needs to do is sit and wait for a passing springtail, or centipede, or woodlouse, or other arthropod to take a step or two across its surface and—bingo!—its ascospores are carried off, later to be deposited somewhere else.

Sticky, ascospore-laden droplets adhere to passing arthropods. 

Along with its special mode of spore dispersal, Catinella olivacea also has peculiar developmental characteristics that are unlike other disc-shaped Heliotales. Interestingly, rDNA studies have now shown that these little guys are more closely related to the Dothideomycetes, which include a large number of plant pathogens, than to the Leotiomycetes, the class that Heliotales belong to.


References:

Catinella olivacea on Mycoquebec

Matthew D. Greif, Connie Fe C. Gibas, Akihiko Tsuneda, Randolph S. Currah, Ascoma Development and Phylogeny of an Apothecioid Dothideomycete, Catinella Olivacea, American Journal of Botany 94(11): 1890–1899. 2007

Two-in-One: Diatrypella betulina and Merismodes confusa/fasciculata

This was a stumper. I'd picked up a couple of white birch branches from the snow because something was obviously growing on them. I recognized the black bumpy eruptions as some kind of a pyrenomycete, or flask fungus, but many of those hard bumpy growths were either partially or fully covered with mysterious, minute, furry brown pellets. Insect eggs? A fungal parasite? I had no idea what they were.

Birch branches with a cup fungus growing on a pyrenomycete.

I took the branches home and stuck one in water to see what would happen. While it was soaking I looked at a sample of the pyrenomycete under the microscope and found numerous wiener-shaped spores clustered together in its asci. This made it a Diatrypella. 

Diatrypella asci produce numerous ascospores.

There aren't a lot of Diatrypella—only 33 named species worldwide. Mine had a green layer inside, which, along with its spore dimensions and birch host made it Diatrypella betulina. One down.

Diatrypella betulina has a green-tinted layer above the perithecia.

I went back to the sample I'd been soaking. The tiny brown knobs had opened into tiny, shallow brown cups, creamy smooth on the inside, and hairy on the outside. 

Water made the hairy knobs open into shallow cups.

Most cup fungi are ascomycetes and, like the Diatrypella, produce their spores in asci. But when I put a thin slice of one of the cups under the microscope I didn't find asci, I found basidia instead. This made identification easier since there are way fewer cup basidiomycete possibilities to choose from than if I'd found a hairy ascomycete.

The spores were like little bratwursts, and some of the cups' outer hairs had bulbous transparent ends. Merismodes confusa (Cyphellopsis confusa), aka Merismodes fasciculata, which is known to grow on Betula, is the closest fit.

Merismodes spores

The tips of Merismodes confusa can be bulbous and transparent.

Merismodes species are known to grow on dead wood in the crowns of trees, and several species not only colonize the stroma of old pyrenomyces, but are known to be most profuse in winter. Referring specifically to Merismodes anomala, which has tubbier spores, Andrus Voitk suggests that it probably requires "dead substrate attachment to living tree tissue." Perhaps that applies to M. confusus/fasciculata as well.

Reference:

Vasilyeva, L.N. and Stephenson, S.L. (2005). Pyrenomycetes of the Great Smoky Mountains

National Park. II. Cryptovalsa  Ces. et De Not. and Diatrypella  (Ces. et De Not.) Nitschke

(Diatrypaceae ). Fungal Diversity 19: 189-200.

Fakirova, V. I.: Pyrenomycetous fungi on a birch (Betula pendula) substratum in Bulgaria. -

Bocconea 5: 839-844.1997

Electronic Atlas of Flora of British Columbia

M. B. Ellis, J.P. Ellis, Fungi without Gills (Hymenomycetes and Gasteromycetes): An identification handbook...

Springer, 1990

 Omphalina: Betula Issue, Vol. IV, No 8