Papalo is an herb native to Mexico and South America, and is most commonly used to top tacos or in salsa. The taste has been described as "somewhere between arugula, cilantro and rue."
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STORE: In a jar on your counter. Fill a jar with cool water, stick sprigs into it, and keep out of direct sunlight. Pick off leaves that will be submerged in water. When stored this way, your herbs should keep fresh for weeks.