Some trees exhibit a striking phenomenon, appearing to “bleed” a red substance from their bark when injured. While it resembles blood, this red secretion is a natural biological process, an intricate part of the tree’s defense and repair mechanisms.
The Nature of the Red Secretion
The red substance flowing from certain trees is a plant exudate, which can be categorized as sap, resin, or latex. Sap is a watery fluid transported through the tree’s vascular system, carrying water, sugars, and nutrients for growth and metabolic processes. It is generally thin and less viscous, serving as the tree’s internal transport system. All trees produce sap.
Resin, on the other hand, is a thicker, often sticky, and more viscous substance produced by specialized cells, primarily in response to injury. Unlike sap, resin is not involved in nutrient transport but functions as a protective barrier, sealing wounds and deterring external threats. Latex is another type of exudate, typically milky in appearance, which also serves a defensive role and is secreted when a plant is wounded. While all trees have sap, only specific species produce resin or latex.
The Chemistry Behind the Red Color
The distinctive red color of these tree secretions comes from specific chemical compounds or pigments. Anthocyanins are water-soluble pigments responsible for red, purple, and blue hues in many plants, including fruits and flowers. These compounds are part of a larger group known as flavonoids, synthesized by plants.
Tannins, particularly condensed tannins, are another group of phenolic compounds that can contribute to the red or reddish-brown coloration. These chemicals are often present in bark and wood, serving as natural protective agents. The specific combination and concentration of these pigments and other phenolic compounds determine the exact shade of red, which can range from a bright crimson to a dark, almost black, reddish-brown.
The Protective Role of Red Secretions
These red secretions play a significant role in the tree’s survival, acting as a defense mechanism against various threats. When a tree’s bark is damaged, the exudate quickly flows to the wound site, forming a protective seal. This process helps to prevent further sap loss and physical damage. The sticky nature of resin can physically trap and immobilize small insects or pests.
Beyond physical protection, the chemical compounds within these secretions possess properties that combat biological threats. Many of these phenolic compounds, including tannins, have antimicrobial and antifungal qualities, inhibiting bacteria and fungi that might infect the wound. Some compounds can also be bitter or toxic, discouraging larger herbivores from feeding on the tree. This multi-faceted defense system allows the tree to heal from injuries and resist environmental pressures.
Trees Known for Red Secretions
Several tree species across the globe are well-known for their striking red exudates, often earning them names that reflect this characteristic. One of the most famous is the Dragon’s Blood Tree, primarily species from the Dracaena genus like Dracaena cinnabari, found on the island of Socotra. This tree produces a deep red resin, historically valued as a dye, varnish, and for its traditional medicinal uses, including wound healing and addressing gastrointestinal issues. Its unique umbrella-like canopy also plays a role in water collection in its arid habitat.
Another notable example is the African Bloodwood tree, Pterocarpus angolensis, native to southern Africa. When its bark is cut, it exudes a vivid red sap that closely resembles blood, giving it common names like “bloodwood” or “kiaat.” This timber species is highly valued for its durable wood and the sap has been traditionally used as a dye and in local medicine for various ailments.
In Australia, species like Corymbia gummifera, known as the Red Bloodwood, also produce a thick, resinous red sap, or kino, particularly when wounded. This characteristic exudate helps the tree recover from damage and is a distinguishing feature of these robust eucalyptus relatives.