Dried Porcini Mushrooms in streams

If I was a leaf, I wouldn’t want to fall into a stream. I’d probably try my hardest to get myself into some kind of a dried flower arrangement, or pressed onto a greeting card as an emblem of autumn. But I would stay away from streams. Streams don’t look like they’d pose much of a danger; after all, they’re just water. But what some leaves don’t realize is that in that water are hundreds of tiny and bacteria just waiting to attack them and break them down, piece by piece, to their simpler elements. And this, for a leaf, must be a very frightening prospect.

A daunting collection of leaf-eating fungi lurks in the waters of freshwater streams. A few are basidiomycetes or oomycetes, but most are ascomycetes and their asexual stages. Stream-dwelling asexual fungi are frequently dubbed Ingoldian hyphomycetes, in honor of the mycologist C.T. Ingold, who first described them in detail. The Ingoldian hyphomycetes include roughly 290 species, including both ascomycetes and basidiomycetes (Shearer et al., n.d.). They are the most commonly studied group of aquatic fungi, and are the main decomposers of hapless leaves that fall into flowing stream waters. You can easily find the spores of Ingoldian fungi by looking in the foam that accumulates in fast-flowing streams–their unique shape (more on that later) means they are easily trapped in bubbles.

Besides the aquatic fungi, streams are also home to some terrestrial  that variously find their way there, often by hitching a ride on leaves or other materials that fall in, or perhaps by tossing their spores into the flowing waters. It has been hypothesized that most aquatic fungi evolved from terrestrial fungi whose spores frequently landed in streams. As a result of this evolutionary history, several genera of fungi, such as Ascotaiwania andAnnulatascus, include both terrestrial and aquatic species