Spellbane Rose (5e Hazard)
From D&D Wiki
These blood-red flowers, also called bloodroses for their wondrous hues and because they grow best when given a small amount of humanoid blood every so often, are found in the ground in 10-foot square patches, though patches are often found adjacent to each other, as spellbane roses grow more swiftly when near other spellbane roses. They emit poisonous pollen that a inhibits a breathing creatures ability to cast magic. Vampires and other sentient undead that do not need to breathe prefer to keep them around to reduce the threat posed by clerics and paladins. Breathing creatures that start their turn standing in or within 5 feet of a patch of spellbane roses must succeed on a DC 13 Constitution saving throw or take 4 (1d8) poison damage and be poisoned for 1 minute. A creature poisoned this way can repeat the saving throw at the end of its turn, ending the effect on a success. A creature poisoned in this way cannot cast spells or use other magical effects, as though it was within the area of an antimagic field. A spellbane rose that is picked retains this property for 1d4 hours, unless preserved with magic.