The white mulberry, Morus alba, is a fast-growing deciduous tree native to China that has been cultivated across the globe for centuries. While the ripe fruit is widely consumed and considered a safe food source, its toxicity is nuanced. Important caveats exist regarding the consumption of the fruit in its unripe state and the other parts of the tree.
The Safety Verdict: Ripe and Unripe Fruit
Ripe white mulberries are non-toxic and have been safely eaten by humans for thousands of years, offering a sweet, often mild flavor. They are packed with antioxidants and vitamins, making them a nutritious addition to the diet. As the fruit fully matures, the compounds that cause adverse effects break down.
The safety concern arises almost entirely from the fruit’s immaturity. Unripe white mulberries, which are typically firm and light green or white, contain a significant concentration of a milky sap, or latex. This latex is the source of the fruit’s low-level toxicity when consumed in large quantities.
Ingesting unripe white mulberries can lead to mild but uncomfortable gastrointestinal distress, including stomach upset, nausea, abdominal cramping, and diarrhea. The unripe berries and raw sap also contain compounds that can stimulate the nervous system, potentially causing mild hallucinogenic effects or intoxication if consumed in excess. These effects are linked to the higher concentration of latex, which diminishes greatly as the fruit softens and develops its mature color.
Concerns Beyond the Fruit: Leaves, Bark, and Sap
The milky sap found in the unripe fruit is present throughout the white mulberry tree, including the leaves, stems, and bark. This sap contains sugar-mimic alkaloids, such as 1-deoxynojirimycin (1-DNJ), which are potent inhibitors of carbohydrate-digesting enzymes. While this compound is used in modern dietary supplements to manage blood sugar, consuming the raw sap or unripe parts of the plant can cause mild irritation to the digestive tract.
Mulberry leaves are widely used, most famously as the sole food source for silkworms. They are also prepared as a traditional tea in various Asian countries and used in supplements. When processed for consumption, the leaves are generally considered safe and may offer a high concentration of fiber and protein. Side effects from leaf extracts are usually limited to mild gastrointestinal issues like bloating or diarrhea.
The bark and root bark of Morus alba have a history of use in traditional medicine, containing prenylated flavonoids and other alkaloids. These parts are not meant for casual consumption and require careful preparation due to the presence of concentrated compounds. The root bark is a source of morusin and kuwanon G, which are typically used only in specific medicinal preparations to mitigate strong physiological effects.
How to Identify White Mulberries (Morus alba)
Accurate identification of the white mulberry tree is important because its name can be misleading. Despite the species name alba (white), the fruit can ripen to a range of colors, including white, pink, red, and dark purple or black. Fruit color alone is not a reliable identification feature, as dark purple white mulberries can be confused with the red or black mulberry species, which are also safe when ripe.
The tree is a fast-growing, medium-sized deciduous tree that can reach heights of 30 to 50 feet. A key identifying feature is the substantial variation in leaf shape, even on a single branch. Leaves can be unlobed (a simple oval or heart shape), mitten-shaped, or deeply three-lobed, with all three forms sometimes appearing together.
The leaves are typically glossy on the upper surface and have serrated edges, distinguishing them from the rougher leaves of the native North American red mulberry (Morus rubra). Another distinctive trait is the milky sap that exudes from a young twig or stem when broken. The combination of highly variable leaves, the presence of milky sap, and the cylindrical fruit shape provide the most definitive visual cues.