The caps of these mushrooms do indeed appear smeared with blood, though it is often hard to see in the dark, damp places in which they grow. Not uncommonly found in Skyrim, their abundance is countered by the difficulty in acquiringthem. As any experienced herbalist knows, the darkest of caves often conceal far more than mere mushrooms.
Nonetheless, these potent fungi, when combined with certain powdered antlers, produce a mixture rendering one quite susceptible to poison. Their usefulness is also quite apparent when mixed with lavender, creating a substance highly resistant to magic.