Photo taken with a cheap digital scope. Soredia are a type of propagule found on lichens. I lichen them to a little 'seedship' made up of a few alga and/or bacteria loosely bound by the hyphae of the fungal partner. These propagules are carried off by wind, water, insects, etc. and contain everything needed to start a new colony if they end up in a suitable habitat. Sometimes soredia are spread out over certain parts of the thallus, but in this case they are being dispersed by the soralia erupting on the ridges of this lichen.
Another type of propagule similar to soredia are isidia. Instead of being a loose bundle, isidia have a cortex encasing the symbiont cells. I imagine this type of propagule lasts longer than one more exposed to the elements. I have always had trouble identifying isidia, I have seen photos of large, warty looking isidia but have yet to see them myself. I'm probably over looking them.
