Palo Azul, or “blue stick” in Spanish, is a traditional botanical ingredient used to make herbal tea. This unique wood has been a fixture in folk wellness practices for centuries, particularly in regions where it grows natively. The resulting light-colored infusion has a subtle, earthy flavor. Growing interest in natural health remedies has led to a renewed focus on this wood.
The Botanical Source
The plant responsible for Palo Azul is botanically identified as Eysenhardtia polystachya, a species commonly known as kidneywood. This designation places the plant within the Fabaceae family. The plant is a thorny shrub or small tree, sometimes reaching heights of up to 20 feet.
The raw material used to create the herbal tea is the wood and sometimes the bark, not the leaves or flowers. The wood is typically harvested and processed into small chips or pieces for brewing. Historically, this wood was known in Europe as lignum nephriticum, a name that references its traditional application in support of kidney health.
Native Habitat and Geographical Range
The native territory of Eysenhardtia polystachya is concentrated throughout Mexico, which remains the largest source of the plant. Its natural distribution extends southward into parts of Central America. The plant’s range also reaches northward into the Southwestern United States, specifically in areas of Arizona and Texas.
This species demonstrates a significant ability to thrive in diverse environments. It is commonly found in arid and semi-arid climates, often growing along the edges of forests and near water courses. The kidneywood tree is highly adaptable, seen at elevations ranging from approximately 490 feet up to nearly 9,800 feet above sea level.
Preparation and the Unique Blue Hue
Palo Azul is typically sold as dried wood chips or small pieces of bark, which are then used to prepare the tea. The process involves boiling or simmering the wood in water for an extended period, often 20 to 30 minutes, to extract the beneficial compounds. A more concentrated brew can be achieved by allowing the wood to simmer for up to an hour or by re-brewing the same wood pieces.
The most remarkable feature of the resulting tea is its natural blue fluorescence, which gives the wood its common name. This unique color is due to the presence of specific compounds in the wood, including flavanoids. These compounds are precursors to a novel four-ringed molecule that is formed through a natural oxidation reaction when the wood is steeped in water.
The infusion does not appear blue on its own but exhibits a striking blue glow when light passes through it, a phenomenon known as fluorescence. For the blue color to be most visible, the water must be slightly alkaline, around a pH of 7.5, as acidic conditions can prevent the reaction. When brewed correctly and poured into a clear glass, the tea visually transforms into a glowing blue beverage under sunlight or bright artificial light.