Reader question: the alien anemones of an orange fungus
The birds are singing and the spores are in the air: it's summer. Plus, plant of the week
And suddenly, as if I’ve walked into a new room while staring at my phone and looked up in confusion, it’s June. Remember all the false starts of summer in April, March, even February? But now we’re done with false starts. This is it. We’re looking at our window AC units and wondering when those get put back in place. The seawater is still cold in the Northeast for at least another month and a half, but effectively, it’s summer—birds breeding, trees leafed out, milkweed getting ready to flower.
Reader question: Just how worried should I be about juniper-apple rust?
Friend of the newsletter Claudia Geib writes in from Cape Cod with an observation of a fungus on a neighborhood juniper tree:
“I've attached here a few pictures of a fungus I observed for the first time ever on my walk through the neighborhood patch of woods … According to iNaturalist, these alien anemones are produced by a fungus called juniper-apple rust, which makes sense since they were all over the Eastern red cedars in this clearing…
I'm so curious about these weirdos and where they came from! Are they native or introduced? Should I be worried about my neighborhood cedars? Is there anything I can do to stop the invasion?
Thanks, Claudia, for the great question, photos, and opportunity to write about a very strange species! “Alien anemones” is just right. Juniper-apple rust (Gymnosporangium juniperi-virginianae) has a specialized life cycle that involves living on different trees at different life stages. It’s a native fungus with a distribution overlapping the North American trees on which it depends. Its scientific name is a reference to the Eastern red cedar/juniper, Juniperus virginiana. Like a shape-shifting parasite in sci-fi, its appearance changes depending on its host. Juniper is a good place to start this cyclical story. In the photo above, spherical galls have grown on a juniper branch, and a spring rain let them extend orange tentacles called teliohorns, which carry spores called teliospores. Each teliospore has two cells and produces four basidiospores—the life stage that carries the fungus to the next host.
The wind can blow airborne basidiospores over a mile to a tree suitable for its next life stage on a tree in the rose family, Rosaceae. While it’s best known for infecting apple and crabapple (Malus) trees, it can also land on hawthorn or fruit plants like pear, quince or serviceberry. On these plants the fungus is less dramatic than on juniper, more rust-like, forming yellowish-brown spots on leaves containing spermogonia for sexual reproduction and exuding a liquid that draws in insects to help fertilize the fungus. New spots on leaves called aecia grow, which release windborne aeciospores that bring the fungus back to junipers.
Even on junipers alone, the fungus’s appearance varies, from the galls with or without their teliohorns (a gall can grow horns and dry out again several times each spring), to elongated shapes known as witches’ brooms, to dabs of orange jelly on a branch called quince rust cankers. A tree covered in galls can start to look like “a tree decorated for the holidays,” writes the Forest Service. One of Claudia’s photos has that holiday ornament look:
Despite its bizarre appearance, the fungus isn’t usually a lethal threat to junipers and typically doesn’t need to be managed. It’s just looking to live on the tree for a while before spreading itself to its next host. Apple and pear farmers are typically on the lookout for juniper-apple rust, cutting down any juniper near the orchard to limit the risk of spread. But even cultivated fruit trees can tolerate a little rust infection—it’s rarely deadly.
If you have a backyard juniper that you want to keep healthy, the only symptom you might want to watch out for is the quince rust cankers. Infected branches swell up and lose their bark. The treatment for quince rust is to prune infected branches, writes the University of Minnesota Extension Office: “The pruning cut should be made several inches below visible signs of the canker to make sure the fungus is completely removed from the tree or shrub.”
And, adds UMN Extension, you can go ahead and knock off those galls for purely aesthetic reasons. The holidays are over, after all. It’s June.
Plant of the week: Buttercup
Back to flowers—I can only take fungi in small doses, to be honest. Buttercups (Ranunculus) have spread themselves over highway medians, parks, and yards the last week, so it’s only fair to reward that effort with plant of the week recognition. My educated guess is that the species is either creeping buttercup (Ranunculus repens) or bulbous crowfoot (Ranunculus bulbosus), both introduced and invasive species that thrive in mowed areas. But seeing them is a good reminder to look for our other buttercup species, many of them native, with more specialized habitat needs, such as small-flowered buttercup (Ranunculus micranthus) which lives in rocky woodlands with fertile soil, or white water buttercup (Ranunculus aquatilis) which has spindly underwater leaves.
Many buttercup species are specialists of wet soils, so a sheltered river bank can be a good place to look for them. The name for the genus means “little frog,” in reference to their love for wetlands.
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Possum Notes is a weekly newsletter about wildlife and landscapes around where I live. It’s produced on occupied Wampanoag and Narragansett land.