Deer Vomit and Sap Yeast
In past years, when the sap would run on our Paper Birch (Betula papyrifera) , I would often notice a pinkish tinge would develop on the sap. But, being pre-iNat for me, it was merely an idle curiosity/observation. This spring after we had the tree pruned, one branch dripped copious amounts of sap and the pink/orangey stuff showed up again. I researched what this might be and it seems as if it's a complex of organisms with the primary ones being Deer Vomit (Fusicolla merismoides) and Sap Yeast (Cystofilobasidium macerans). I thought I might as well save what I found in a journal post for any future reference.
April 2024 observations
The sap dripped so heartily from this pruned branch that it created puddles in the grass under it. The slimy substance grew on the open wound of the branch and in the grass under it.
https://www.inaturalist.org/observations/209760280
https://www.inaturalist.org/observations/211160256
https://www.inaturalist.org/observations/211160251
Research
Infrequently in the spring, you might see an orange, slimy substance slowly oozing from a wound on a hardwood tree. This is a fungus or a complex of fungi and yeast that colonize the sap that leaks from a tree wound. The primary fungus involved that gives this slime its orange color is Fusicolla merismoides (formerly called Fusarium merismoides). | Clemson Cooperative Extension; "FUSICOLLA ORANGE SLIME ON TREES"; Apr 2, 2020; Joey Williamson
Our little yeast is called Cryptococcus macerans, a basidiomycete yeast first discovered in Denmark, mostly found in sweet wild fluids in frigid parts of the globe such as Iceland and Patagonia and now from wherever it is I live. The orange pigment is of course carotene, the same chemical that colours carrots. This is one of a group of yeasts that really don’t like each other yeasts very much. They slaughter each other with killer toxins called mycocins. There are other species in this slime, including moulds like Fusarium and that musical-sounding Acremonium. | Cornell Mushroom Blog; April 30, 2010
If you have ever seen gooey neon orange branches on trees and shrubs you may have been observing a phenomenon commonly known by the very scientific name of ‘orange goo’. Appearing in cool, wet weather during spring sap flow, the goo is caused by fungi, bacteria and yeast colonizing tree sap, especially where an injury causes excessive sap flow. Orange goo (or slime if you prefer) has been reported on a wide range of trees and shrubs from across the US and Europe. Those who have studied the phenomenon have generally reported the main cause of the orange color is a yeast in the genus Cryptococcus, which accumulates carotene, the same pigment found in carrots. Others have reported a number of different Cryptococcus spp. in spring sap-flows as well as several Fusarium species and Fusicolla merismoides. The composition of the fungi and yeasts present may differ from location to location and may change over time as temperatures increase. | Purdue University; "Orange Goo – Dramatic but Harmless"; May 24, 2022; Tom Creswell
comments or corrections welcome
