Rose rust fungus. Coloured environmental scanning electron micrograph (ESEM) of the rose rust fungus (Phragmidium sp.). Its spores (yellow/brown, at upper centre for example) are also seen. Rust fungi are common parasites on both wild and cultivated plants, causing rust-like patches to develop on the leaves and stems. They are extremely host specific, and many species have highly complex life cycles. Unlike a conventional scanning electron microscope (SEM), samples placed into an environmental SEM do not need to be desiccated or coated in gold. Magnification unknown.