Apiosporina morbosa

April 18, 2022

Good evening, friends,

This week’s mushroom is Apiosporina morbosa, formerly known as Dibotryon morbosum, and commonly known as black knot. While technically not a mushroom, this is still an interesting fungus with which we can familiarize ourselves. The below specimen was found up in Manitou on 3/7/2022, and what’s more curious is that there is a stark lack of this fungus in Central Park.


A. morbosa is an ascomycete – a different phylum of fungus than the normal gill/toothed/poroid basidiomycetes we often encounter. It is parasitic on trees in the genus prunus – including plums, cherries, peaches, almonds, and other nutritious tasties. This specimen was found growing on black cherry (Prunus serotina). A. morbosa is found throughout North America, particularly east of the Rockies. You can find the knots year-round so it’s a good species to know this time of the year when fungal finds can be few and far between.

Instead of trying to explain the ~2 year lifecycle of A. morbosa, I’m including a diagram below from the Cornell Cooperative Extension Integrative Pest Management (reference 2):

In the image below you see how the knots can blister and strip stems of their xylem and phloem, killing the branch. A. morbosa is typically not fatal, but if you have a plum or peach orchard that gets infested you may wish it were…for you. Dark.

The below picture shows how all the saplings in the area were afflicted:

What’s peculiar is that black cherry (Prunus serotina) is the most common tree in Central Park, yet I don’t recall encountering these knots at all. This made me think of how the park’s American Elm trees (Ulmus americana) were partially isolated from Dutch Elm Disease (a fatal disease caused by the non-native, pathogenic fungus Ophiostoma novo-uli spread by beetles). There can be an advantage to being on an island and surrounded on all sides by grey infrastructure. Albeit, the park loses a handful of elms every year to DED, and there are a few observations of A. morbosa in the park on iNat, but it appears that there are fewer cases in CP than there are in the outer-borough parks.

Here are a couple finds from Manitou this past Friday:

Xeromphalina spp.
Sarcoscypha spp.

I’ve got a feeling we may start seeing morels pop up in Manitou soon – I scrupulously searched today to no avail – and they very well may already be in Central Park. The president of the New York Mycological Society, Sigrid Jakob, uploaded a black morel (Morchella angusticeps) on iNaturalist this weekend. Looking on the ground around tulips, dying elms, sycamores, and hickories is a good start. Happy hunting!

Have a spectacular Earth Day this Friday,

1) Kuo, M. (2021, March). Apiosporina morbosa. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/apiosporina_morbosa.html
2) https://ecommons.cornell.edu/bitstream/handle/1813/43075/black-knot-plum-FS-NYSIPM.pdf?sequence=1&isAllowed=y
3) https://web.extension.illinois.edu/hortanswers/detailProblem.cfm?PathogenID=86
4) https://hort.extension.wisc.edu/articles/black-knot-apiosporina-morbosa/