Lablab purpureus, commonly known as hyacinth bean, field bean, or in Sinhala as me karal, is one of the most versatile leguminous plants cultivated across South and Southeast Asia. In Sri Lanka, it holds a respected place in both traditional agriculture and the island's long-standing Ayurvedic healing system, where it is catalogued among the medicinal plants used in indigenous treatment practices.
What is Lablab purpureus?
Lablab purpureus belongs to the family Fabaceae and is thought to have originated in Africa, though it has been cultivated on the Indian subcontinent for thousands of years. The plant is a twining annual or short-lived perennial vine that produces trifoliate leaves, purple or white flowers, and flat, curved seed pods. Both the immature pods and the mature seeds are edible, and virtually every part of the plant — leaves, flowers, pods, seeds, and roots — has documented uses in traditional medicine.
The seeds vary in colour from white and cream through to dark purple or nearly black, depending on the cultivar. In Sri Lanka, multiple landraces are grown, each adapted to different agro-climatic zones, from the dry lowlands of the North Central Province to the wetter intermediate zones.
How is Lablab purpureus used in Ayurveda?
Within the framework of Sri Lankan Ayurvedic medicine, Lablab purpureus is valued for several therapeutic properties. Practitioners traditionally use preparations derived from the seeds and leaves to address digestive ailments, inflammation, and general nutritional deficiencies. The plant is considered to have cooling properties in Ayurvedic constitutional theory, making seed-based formulations relevant in conditions associated with excess heat or pitta imbalance.
The leaves are sometimes applied as poultices in folk medicine for minor skin conditions, while the seeds — once properly processed to reduce naturally occurring toxic compounds such as cyanogenic glycosides — are used in both food and medicinal preparations. It is important to note that raw or undercooked seeds should not be consumed in quantity; traditional processing methods, including prolonged soaking and boiling, are standard practice across Sri Lanka and India.
Alongside other documented medicinal plants such as Pongamia pinnata and Acacia chundra, Lablab purpureus contributes to the breadth of Sri Lanka's botanical pharmacopoeia, which encompasses hundreds of species used in classical and folk healing traditions.
What nutritional value does Lablab purpureus offer?
From a nutritional standpoint, the dried seeds of Lablab purpureus are a meaningful source of plant protein, dietary fibre, and several micronutrients including iron, calcium, and B vitamins. This makes the crop particularly valuable in subsistence-farming contexts, where it supplements staple cereals and contributes to household food security.
The immature green pods are eaten as a vegetable across Sri Lanka, prepared by boiling, stir-frying, or incorporating into rice-and-curry meals. The tender leaves are also cooked as a green vegetable in some rural communities, much as one might use spinach or drumstick leaves.
- Protein content: Mature dried seeds typically contain around 20–25 g of protein per 100 g dry weight, comparable to other common legumes.
- Dietary fibre: High fibre content supports digestive health, consistent with its traditional use in managing gastrointestinal complaints.
- Anti-nutritional factors: Raw seeds contain lectins and cyanogenic compounds; thorough cooking neutralises these effectively.
Where is Lablab purpureus grown in Sri Lanka?
The crop is widely distributed across the island's dry and intermediate zones, where it is grown both as a primary crop and as a secondary crop intercropped with maize, sorghum, or finger millet. It is well adapted to low-fertility soils and requires relatively modest water inputs compared to other legumes, making it a practical choice for smallholder farmers in areas with a pronounced dry season.
In the ancient agricultural landscapes around Polonnaruwa, traditional mixed farming systems have long incorporated leguminous crops like Lablab purpureus to restore soil nitrogen between paddy seasons — a practice with deep historical roots in Sri Lankan agrarian culture, also reflected in the management of traditional paddy fields (kumbura).
Home gardens throughout the country also cultivate the plant, often training it over fences or simple trellises, where its purple flowers and glossy pods provide both food and a degree of ornamental value.
What is the ecological role of Lablab purpureus?
As a legume, Lablab purpureus forms a symbiotic relationship with nitrogen-fixing bacteria in the genus Rhizobium, enriching the soil for subsequent crops. This characteristic has made it a standard component of cover-cropping and green-manure systems in tropical agriculture. In Sri Lanka, its use in this capacity aligns with traditional agronomic knowledge that predates modern soil science by centuries.
The plant is also browsed by livestock and is occasionally cultivated specifically as fodder, offering a dual-purpose crop well suited to mixed farming households. Its rapid growth and tolerance of drought conditions further enhance its ecological and economic utility in the drier regions of the island.
How does Lablab purpureus fit into Sri Lanka's broader plant heritage?
Sri Lanka's rich tradition of ethnobotany means that plants like Lablab purpureus are understood not in isolation but as part of a living knowledge system. The island's Ayurvedic physicians, known as veda mahattayas, have maintained oral and written records of plant usage across generations. Government institutions including the Department of Ayurveda formally catalogue such species, and Lablab purpureus features in the official pharmacopoeia of Sri Lankan medicinal plants.
Visitors interested in exploring this botanical heritage may find relevant context in Sri Lanka's spice-growing regions and traditional homesteads, where plants like Syzygium aromaticum (clove) and Cocos nucifera (coconut) grow alongside food legumes in the layered structure of a traditional home garden. Such gardens represent a practical, living library of the island's medicinal and nutritional plant knowledge.
Conservation and continued relevance
Despite its long history of cultivation, traditional landraces of Lablab purpureus face pressure from the adoption of uniform commercial varieties. Conservation of genetic diversity within this species is considered important by researchers and development organisations working on food security across South Asia. In Sri Lanka, seed-saving practices among smallholder farmers have helped preserve locally adapted varieties, though formal gene-bank programmes play an increasingly important backup role.
Interest in Lablab purpureus has grown in recent years within global food science and nutrition communities, partly due to renewed focus on under-utilised crops capable of contributing to sustainable diets. Its drought tolerance, soil-improving properties, and nutritional density position it as a crop relevant to climate adaptation strategies in tropical regions.
