USDA Forest Service, Northern and Intermountain Region , USDA Forest Service, Bugwood.org
Wikimedia Commons
Description: English: Spores of Melampsora medusa on a leaf of eastern cottonwood (Populus deltoids). Date: 13 November 1995. Source: https://www.forestryimages.org/browse/detail.cfm?imgnum=2251096. Author: USDA Forest Service, Northern and Intermountain Region , USDA Forest Service, Bugwood.org.