Uredinium

Part of speech: noun

Definitions

1. A small cluster-forming structure on a rust fungus that produces repeating spores during the infection cycle on a host plant
2. The rounded, powdery pustule formed by certain rust fungi that releases asexual spores onto the leaves or stems of plants
3. A fungal fruiting body of the rust group that generates summer spores capable of spreading the infection from plant to plant

Etymology: Uredinium names a cluster of spores produced by rust fungi, the plant pathogens that leave orange or brown powdery pustules on leaves and stems. The word is a modern scientific coinage built from Latin "uredo," a term for a blight or burning of crops, with the added ending "-ium," which in botany marks a structure or fruiting body. The Latin root itself points to the destructive effect on plants, since "uro" means "to burn," an image that fits the scorched look of an infected leaf. The Latin "uredo" has the stem "uredin-," which is why the English word takes the form it does: the base of the Latin noun is combined with the "-ium" ending rather than the full nominative form. Mycologists used this pattern to name the distinct spore stages of rust fungi, each stage given its own term.