Many plants are known as “milk plants” due to the milky white, often sticky fluid that oozes from their stems or leaves when damaged. This fluid is scientifically known as latex. The presence of this unique sap is a common characteristic across diverse plant families and habitats.
Understanding Milky Sap
The milky sap, or latex, is a complex emulsion containing proteins, alkaloids, starches, sugars, oils, tannins, resins, and gums. While white, it can also appear yellow, orange, or clear in some species. Latex is produced and stored within specialized cells called laticifers, which form tube-like structures throughout the plant.
The primary function of milky sap is defense. When a plant is injured, latex leaks out under pressure, forming a physical barrier that deters herbivores by gumming up their mouthparts or being unpalatable. The sap’s chemical components, often toxic, also act against pathogens like fungi and bacteria, aiding wound healing and preventing infection. This defensive mechanism has evolved independently in many plant families.
Diverse Examples of Milk Plants
Many common plants produce milky sap. Milkweed (Asclepias species) is a well-known example, exuding milky latex when stems or leaves are broken. Most milkweed species share this characteristic, except for butterfly milkweed (Asclepias tuberosa).
The Euphorbia genus also features milky sap, including ornamental plants like poinsettia, pencil cactus (Euphorbia tirucalli), and crown of thorns. Various Ficus species, such as the common fig (Ficus carica), rubber plant (Ficus elastica), and fiddle-leaf fig, release a white, sticky sap when damaged. Dandelion (Taraxacum officinale) also produces a milky substance. The Para rubber tree (Hevea brasiliensis) is cultivated specifically for its latex, the primary source of natural rubber.
Ecological Roles and Human Uses
Milk plants play various ecological roles. Milkweed, for instance, is a host plant for Monarch butterflies, whose caterpillars feed exclusively on its leaves. The plant’s compounds make Monarchs toxic to predators. These plants also contribute to biodiversity by providing nectar for pollinators and habitat for other creatures.
Humans use the sap or the plants themselves in various ways. Natural rubber production from the latex of the Hevea brasiliensis tree is the most prominent industrial use. Historically, milky sap from some plants was used in traditional medicine for ailments like wound healing or as diuretics, though often with caution due to its potent nature. Many milk plants are also valued ornamentally, with Euphorbias and Ficus species popular for gardens and indoor spaces.
Safety and Handling Precautions
The milky sap of many “milk plants” can be irritating or toxic. Skin contact can cause irritation, redness, and blistering, especially when exposed to sunlight (phytophotodermatitis). If sap enters the eyes, it can lead to severe pain, inflammation, blurred vision, or temporary blindness. Ingesting the sap can cause burning sensations in the mouth, throat, and stomach, along with gastrointestinal upset, vomiting, and diarrhea.
When handling plants that produce milky sap, wear protective gloves to prevent skin contact. Avoid touching your face, especially your eyes, during and after handling. Wash hands thoroughly with soap and water immediately after contact to remove residual sap. Keep milk plants out of reach of children and pets to prevent accidental exposure or ingestion. If severe reactions occur from contact or ingestion, seek prompt medical attention.