The article Keru: The Tree That Waterproofed Time and Once Held Civilizations Together by Dr. Satyanarayana Bhat in the Native Circle knowledge repository explores the deep historical and cultural significance of the Keru tree (Semecarpus anacardium), also known as the Marking Nut Tree. Once a cornerstone of indigenous Indian technology, the tree’s unique properties connected forests to architecture, medicine and ritual. Excerpt of the article Key traditional applications of Keru Architecture & Waterproofing: Long before modern sealants, Keru oil was used to waterproof temple towers, fort walls, and household floors. It provided a natural barrier against the intense monsoons of the Western Ghats. Agriculture: The oil served as a preservative for bamboo and reed-based agricultural tools (like winnowing baskets), making them termite-proof and durable for generations. Medicine: In Ayurveda, despite its ability to blister skin, the nut was purified and used to treat severe hair loss and skin conditions. Sacred Rituals: The tree played a role in Shaiva traditions and Rasavaidya (Indian alchemy), particularly in the creation and preservation of Ishtalingas (sacred objects worn on the body). A fading memory residing as oral histories The indigenous Keru in the longer run was replaced by the cashew tree (referred to as Turuka Geru or "foreign Geru"), which was introduced later but became more commercially accessible. Much of the sophisticated "material intelligence" required to process the toxic Keru nut safely has faded, surviving now only in oral histories among communities of scattered geographies — Karnataka, Maharashtra, temple towns, itinerant communities, forest edges and agricultural settlements. The story of Keru serves as a reminder that indigenous knowledge was not merely "folklore" but a highly evolved relationship with the environment. The tree represents a time when forests were viewed as laboratories and pharmacies, providing sustainable solutions for civilization’s most basic needs. To read the complete article, click here.