Demontrumpets

Description:

Demontrumpets grows to 12-18 inches at full growth. It has rather dark green foliage and herbaceous stems. It tends to spread slowly but is incredibly resilient. When it flowers it produces six downturned, blood red flowers. It has a fairly sweet aroma, but if it plucked or damaged, a nasty, graveyard smell is released. PAtches of these plants will grow to about 6' in diameter.

The plant itself is non-toxic, but no creature that smells is likely to eat it. The smell only gets worse when cooked or left to rot.

The plant is restricted to reasonably warm climates, not able to survive a hard frost.

Growth Cycle:

Demontrumpets expands only through slow, but very deep and long runners. These travel underground at a rate of about 100' per season, and will randomly breach the surface every 2-3 years where a new plant will emerge.

Magical Properties:

Demontrumpets, as illuded to by the name, are not normal plants, but are plants who hold their origin in the Abyss. Perhaps brought by summoned demons, perhaps created by a dark god for some purpose, perhaps simple plants mutated by an artifact of great evil. As such they have a link to that place and exude a powerful aura of evil. Touching the plant, or ingesting it have the same effects as touching or ingesting unholy water. The area withing 3' radius of the plant should considered unholy ground and corpses in this area have an increased likelihood of rising as undead.

The effect is so strong that even small brooks which pass close to a patch will acquire the unholy taint for at least 10' downstream.

Uses:

This plant is very useful in the fields of Diabolism and Necromancy, as well as in warding magic against good aligned powers.
It can be used to prepare unholy water without the assistance of the necessary clergy, as well as for making dreadfully effective stink and nausea compounds.

PlotHooks:

Whoops
While running through the forest, either in pursuit or being pursued, the PC's Cleric/Paladin stomps through a patch of Demonstrumpets and falls down in pain. The other PC's run through the same plants with no effect.

Hunting for Herbs
The party is contracted by an Alchemist who is generally thought of as a reasonably good person to acquire some of the herb (perhaps he calls it something else, but gives the same physical description), especially if the alchemist thinks there are no specifically pious members in the party. How will they react when they finally get their hands on the plant? What good person would use this stuff. Bringing the herb home may be difficult as well as the released stench may be a problem.

Unintended consequences
A group of humanoids have discovered part of the plants properties and cultivated a wide band of the plants to act as defence - if an enemy walks through it, they would smell the stink of the disturbed plant. Unfortunately for them, the plant spread to the tribe's grave-pit and a large number of undead rose. The humanoids (variety of your choice) were destroyed by the undead, and now their tribe's camp is swarming with undead.

False Alarm
The party camps for the night near a patch. One of the tied up horses stomps the plant and the sudden graveyard stench wafts across the campsite. The PC's prepare for an undead attack that never comes.