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