Photo and description from Strictly Medicinal Seeds (www.strictlymedicinalseeds.com).
(White Horehound) Herbaceous perennial native in the Mediterranean basin and Asia, having naturalized worldwide, widespread in the American SW. Traditional usage (TWM): cough and sore throat. Plant prefers full sun and dryish, nutrient-depleted soils. This is a plant that can literally be killed with kindness, so allow it to grow on the margins of the garden where water and nutrients grow thin. Transplant to 1 foot apart–they are somewhat diminutive and will grow only about as tall as your knees.