Melastoma is a plant genus of about 50 unique species of flowering shrub-like plants. These plants are indigenous to countries with tropical climates, and are particularly abundant in southeast Asia, India, and Australia, where they are usually found growing wild in forested areas or meadows. Melastoma shrubs are popular decorative plants due to their attractive purple flowers, and are planted in gardens around the world. Their popularity as ornamental plants, combined with their adaptability and fast growth, has resulted in the plants being labeled as pests in many areas, particularly in the United States, where many states prohibit the import of seeds or seedlings. The shrubs also have a wide range of culinary uses, as their leaves, stems, and fruits are all edible, and have been used in traditional herbal medicine.
Plants of the genus Melastoma are medium- to large-sized flowering shrubs that can achieve heights of up to seven feet (two meters). The shrubs have dark green, tapered, oval leaves. Most species are evergreens, meaning that their leaves do not fall at the end of each growing season. Melastoma plants are well-known for their eye-catching flowers, which are usually a soft lavender color with many layers of petals. These shrubs also produce blue or dark purple edible fruits that have a watery, bland flavor, and turn the mouth of the person eating them a deep blue color — a quality that has given the plants the alternate name "blue tongue."
Many species of Melastoma are considered invasive weeds. Even in their native habitat, the plants frequently spread into land occupied by industrial forests of rubber or mahogany trees, which can be damaging to production levels. In the Hawaiian islands, the plants were originally planted in gardens, but quickly spread outside of their controlled environment, supplanting many native flower species.
In many southeast Asian countries, the plant parts of Melastoma shrubs are used in cooking. While the fruits of the plant tend to be rather tasteless, its stems and leaves have a pungent, tangy flavor. The leaves may be served cooked or raw. In Indonesia, the leaves and stems of the shrub are cooked together with starch and sugar syrup to make a confection known as grass jelly. Grass jelly has an herbal flavor reminiscent of lavender and may be eaten as a dessert, or added to fruity drinks as a sweetener.
Some species of melastoma also appear to have beneficial effects on the digestive system. Therefore, the plant is sometimes used in traditional herbal medicine. When ingested, it can be helpful in treating indigestion, diarrhea, and dysentery. It can also be made into a salve or wash that can be applied topically to hemorrhoids.