“Guttation!” I muttered with delight

As a linguist, I never met a new word I didn’t like, and “guttation” is no exception.*

I unearthed this splendid word when I was trying to understand what I was seeing on the surface of a crusty fungus growing all over a dead log:

It was oozing droplets, a few clear, many amber, and some black and tarry:

I eventually identified this fungus tentatively as Ionotus glomeratus. It doesn’t seem to have a common name.

The mechanism of guttation in plants is better studied than in fungi. Here is a strawberry leaf, exuding droplets of sap from the tips of its leaves:

When the ground is saturated, and the leaf is still growing the water pressure forces the sap up through the xylem until it sweats droplets from small structures called hydathodes. It happens mainly at night, when transpiration is suppressed, so it is best seen early in the morning. The liquid is not plain water, but is rich in sugars and potassium, so many insects consume it as an important part of their diet.

In fungi, we know less, but it is clear that the liquid here is also not just water, but contains a range of secondary metabolites. This unidentified mushroom is exuding a clear liquid.

And this Hemlock Varnish Shelf seems to be bleeding:

PS * The word “guttation” comes from the Latin gutta, meaning a drop of liquid. It has survived with its meaning essentially unchanged in many Romance languages: French as goutte, Spanish as gota, and Italian as goccia.

PS Not all plants do this, and nor do most fungi. The reasons are mysterious. In fungi, the droplets contain all sorts of chemicals, some of which seem to be poisonous to competing fungi. But their place in the ecosystem is still largely a mystery. Krain and Siupka 2021 say “researchers have already found numerous mycotoxins, antimicrobials, insecticides, bioherbicides, antiviral, and anticancer agents in exudate droplets. They belong to either secondary metabolites (SMs) or proteins and are secreted with different intensities.“