Hi Karma,
Not enough info to help you, but it sounds like the soil stayed too wet at some point.* I just did that with some basil I rooted.* I potted up the rooted cutting and it was doing great.* I watered it a couple of days ago and forgot to empty the water in the saucer.* Today I noticed the stem was black and the leaves are all wilted and there was still water in the saucer.* Even with all I know it can happen when you get distracted.* :?*
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.