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
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.
Cedar apple rust infecting an apple tree (Malus domesticus). Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.
Roughly 75 people in North America are poisoned each year by mushrooms, often from eating a poisonous species that resembles an edible species. Though deaths are rare, there is no cure short of a liver transplant for severe poisoning. Don't eat any mushroom unless you are absolutely certain of its identity! Please don't trust the identifications on this site. We aren't mushroom experts and we haven't focused on safely identifying edible species.
Gymnosporangium macropus Link
Gymnosporangium virginianum Sprengel
Gymnosporangium juniperi-virginianae description by Thomas H. Kent, last updated 6 Sep 2021.