Cedar Trees Grow Apples, Too (but please don’t eat them)

by Anna Boggs, Rural Retreat, VA | Oct 1, 2022 | 0 comments

“Hey, let’s see if there’s a nest in here,” I said to my little sister. We had accidentally frightened a pair of Mourning Doves from a stout cedar tree. The wide-eyed birds went whistling away to another tree to watch from a safe distance.

Elizabeth pushed the conifer’s sparse, needled branches aside in search of the chaotic pile of sticks the Mourning Dove is known for. No sooner had our eyes adjusted to the dim interior of the tree than I saw something else I was definitely not looking for!

“Aah! What is that?!” I jumped back, startled, to say the least. Dubious, I leaned as close as I dared to the thing. “What on earth?”

Clinging nonchalantly to a cedar branch, the object of my suspicion looked like something from a foreign jungle—dullish brown, slightly spherical in shape, and just a bit larger than a golf ball. What made it so freakish were dozens of short, dry, dark brown spikes punctuating its surface. It looked like something that would explode if you touched it.
Curiosity overcame suspicion, and we plucked the branch for research purposes. Gingerly holding the thing at arm’s length, we made our way home. Upon researching, we discovered something with peculiarities beyond its alien-like appearance.

Cedar-apple rust, named for its orangish-red color, is a widespread fungus common to the eastern United States and Canada. This oddity’s favorite habitat consists of both farmland and forest. In order to complete its life cycle, cedar-apple rust relies on not one, but two (or more) different hosts, usually a juniper and an apple species. It also depends on wind to carry it from one to the other. The warm rains of early to mid-spring kickstart one of its many developmental stages, which include the production of four different types of spores.

This wacky fungus begins its cycle as spiky brown galls on the branches of a cedar tree. The spikes, known as telial horns or teliohorns, are activated by the warm spring rains, which cause them to grow long and become gelatinous, like tentacles made of Jell-O®. Their color changes from a dull rust color to a flaming neon orange, giving them a truly otherworldly appearance. Five to seven sets of teliohorns develop each spring, one after each rainfall.

The wet teliohorns now produce the first spores in the cedar-apple rust cycle, the teliospores. These spores then germinate and form reproductive structures known as basidia. (This feature places the rust in the family Basidiomycota, a large group containing many common mushrooms.) The basidia produce basidiospores—spore number two. The basidiospores are released into the wind. They may travel 2-3 miles (3-5 km) this way.

Cedar-apple rust
Cedar-apple rust. Photo © Dreamstime.com.

Those that come to rest on the leaves and fruit of apple or hawthorn trees germinate and create yellowish lesions on the leaves and fruit of the host tree. These lesions form spermogonia (another kind of reproductive structure) which in turn produce yet another and the third spore, spermatia. The spermatia are released in a sticky substance that attracts insects. The insects, by default, perform fertilization by carrying the spermatia on their bodies and transferring them to other lesions in the area as they feed.

Once fertilized, the lesions grow through the leaves and form another reproductive structure called aecia, which produce aeciospores—the fourth and final spore in the cedar-apple rust’s life cycle. The aeciospores are carried by the wind back to the original host, where they germinate in the cedar’s branches to begin the formation of the galls which will produce next year’s crop of teliohorns, thus perpetuating the cycle of this decidedly weird fungus.

Cedar-apple rust and other members of the rust family are vicious attackers of junipers, apples, and many other crops and trees. If an infestation becomes especially heavy, the infested trees become weakened and often die. Typically, in areas where apples are grown, junipers are felled within a radius of two or three miles to prevent the infection of the apple trees.

After researching the whereabouts of our fungus find, we decided to dissect it. I expected the thing to squish like a marshmallow, but instead, it proved firm and porous, like an apple. It was even pale green inside, resembling a Granny Smith.

What an extraordinary discovery on a very ordinary walk on an equally ordinary day! Who knew cedar trees could grow apples?!

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