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Gymnosporangium juniperi-virginianae Schwein. 1822

Cedar apple rust, American apple rust

KingdomFungiMushrooms, lichens, gel fungi, yeasts, and molds; also called eukaryotes
DivisionBasidiomycotaA group containing a staggering 31,000 living species, encompassing rusts, smits, and many fungi
ClassTeliomycetesFungi in which a sorus develops in place of a basidiocarp
OrderUredinalesFungi causing various rust diseases in plants
FamilyPucciniaceaeParasitic fungi causing rust diseases in plants
GenusGymnosporangiumGenus of fungi that produce galls on cedars and other conifers of genera Juniperus and Libocedrus and causes rust spots on apples and pears and other plants of family Rosaceae
Speciesjuniperi-virginianaeThe species of conifer, Juniperus virginiana or eastern redcedar, infected by this rust

About plant names...

Cedar apple rust lives out part of its life on two different species of trees (making it a heteroecious parasite). Each of the trees, eastern redcedar and apple trees, must be fairly close together. (Sometimes the fungus inhabits quince or hawthorn instead of apple trees.)

Identification: This fungus transmutes itself through several stages of development. In the phase where it takes up residence in eastern red cedar, it produces uneven light brown sacs about an inch around. The sacs become rounder and resemble an oak gall. That is, until they begin pushing out orange columns, creating a structure that looks a little like a rusty World War II mine. The columns continue to exude, becoming a Medusa-like cluster of orange, slimy tentacles. The tentacles are actually “spore horns,” and they release spores that develop for a time and become airborne. Some of these land on apple trees, where they grow, coating the leaves with an orange-yellow blister-like “rust.” This in turn eventually releases more spores that infect new eastern red cedars, continuing the cycle. For a more detailed explanation, see Tom Volk’s description.

Gymnosporangium juniperi-virginianae (cedar apple rust, American apple rust)

Spore horn stage of cedar apple rust. By Dr. Brendan Hodkinson. Chapel Hill, NC. 4/15/2010.

Cedar apple rust does substantial damage to apple trees, and is considered an invasive species in some regions.

Gymnosporangium juniperi-virginianae (cedar apple rust, American apple rust)

Cedar apple rust infecting an apple tree (Malus domesticus). Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.

Edibility: Please tell me you’re kidding!

Online References:

Gymnosporangium juniperi-virginianae on Tom Volk's Fungi site, at the Department of Biology at the University of Wisconsin

Gymnosporangium juniperi-virginianae on Squamules

Gymnosporangium juniperi-virginianae on Michael Kuo's MushroomExpert.com

Gymnosporangium juniperi-virginianae on extension.illinois.edu

Gymnosporangium juniperi-virginianae on Wikipedia

Gymnosporangium macropus Link

Gymnosporangium virginianum Sprengel

 

Gymnosporangium juniperi-virginianae description by Thomas H. Kent, last updated 6 Sep 2021.

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Gymnosporangium juniperi-virginianae (cedar apple rust, American apple rust)

On eastern redcedar (Juniperus virginiana) · 4/3/2011 · Susan & Raimond’s, Phoenix, Mary­land
≈ 4½ × 3" (11 × 7.9 cm)

Gymnosporangium juniperi-virginianae (cedar apple rust, American apple rust)

On eastern redcedar (Juniperus virginiana) · 10/5/2010 · Susan and Raimond’s, Phoenix, Mary­land
≈ 6 × 4" (15 × 10 cm)

Gymnosporangium juniperi-virginianae (cedar apple rust, American apple rust)

Front and back of an infested crabapple leaf. · 8/24/2021 · Tom and Susan’s, Highland Green, Topsham, Maine

Gymnosporangium juniperi-virginianae (cedar apple rust, American apple rust)

On eastern redcedar (Juniperus virginiana) · 10/5/2010 · Susan and Raimond’s, Phoenix, Mary­land
≈ 5 × 3½" (13 × 9.2 cm)

Gymnosporangium juniperi-virginianae (cedar apple rust, American apple rust)

7/15/2011 · Susan and Raimond’s

Range:

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