Possible Clues:

• Number brought over and let loose in plant
• A weed to annoy
• '''Grasp a . . . . . . firmly and it will not sting
• Upset sample of herbal tea?
• Clasp it firmly and it will not sting
• No strings on it - just stings
• And in Latin during Lent this has a sting to it
• Sting
• Sting(er) - annoy
• A weedy type, and stingy