Creeping Charlie, or ground ivy, is toxic, but generally horses must consume large quantities for a reaction to occur. | Photo Credit: Kaldari/Wikimedia Commons

Life Cycle: Creeping perennial
Origin: Eurasia
Poisonous: Yes

Ground ivy is distributed widely across the United States, except for in the desert Southwest. It grows in lawns, flowerbeds, and pastures. Horse pasture infestations are more severe during overgrazed or other conditions that inhibit grass growth.

Ground ivy is a member of the mint family that creeps along the ground and can grow to three feet or more in length. The stems are square, and flowers are a reddish-purple