A cashew is not a legume. Botanically, cashews are tree fruits, specifically drupes, while legumes belong to the pea family, Fabaceae. This distinction often causes confusion because of the common culinary use of “nut” for various plant parts and the similar appearance of some seeds. Understanding the precise botanical classification clarifies these differences.
Understanding Legumes
Legumes are plants belonging to the pea family, known scientifically as Fabaceae. A defining characteristic of legumes is their fruit, which is typically a pod that splits open along two seams to release its seeds. These seeds, when dried for human consumption, are often called pulses.
Many legumes also possess a unique biological feature: they form a symbiotic relationship with specific bacteria called Rhizobia in structures known as root nodules. These bacteria convert atmospheric nitrogen into a form usable by the plant, a process called nitrogen fixation. This natural fertilization enriches the soil and is a significant reason why legumes, such as peas, beans, lentils, and peanuts, are agriculturally important.
Understanding Cashews
The cashew, scientifically known as Anacardium occidentale, is a tropical evergreen tree in the family Anacardiaceae, which also includes mango and pistachio. What is commonly called a “cashew nut” is botanically a single seed contained within a kidney-shaped structure called a drupe. This drupe grows at the end of a fleshy, pear-shaped structure known as the cashew apple, an accessory fruit that develops from the flower’s stem.
The cashew tree is native to northeastern Brazil and thrives in warm, tropical climates. The drupe, containing the cashew seed, develops first, followed by the expansion of the flower stalk to form the cashew apple. Unlike legumes that grow in pods, the cashew’s seed is encased within a hard, toxic shell inside the drupe, requiring careful processing before consumption.
Why Botanical Classification Matters
Knowing the botanical classification of foods holds practical implications for consumers. One significant area is food allergies, where cross-reactivity can occur between botanically related species. While cashews are tree nuts and peanuts are legumes, individuals with a peanut allergy do not automatically have a tree nut allergy, though co-sensitization can happen. There is a recognized high rate of cross-reactivity between closely related tree nuts, such as cashews and pistachios, due to shared proteins.
Understanding these classifications also informs nutritional considerations. Legumes are rich in protein and fiber, with a lower fat content compared to many tree nuts. Tree nuts, including cashews, have a higher fat content, primarily unsaturated fats, and are more calorie-dense. This botanical knowledge allows for more precise dietary choices and helps avoid misconceptions that could impact health or dietary planning.