Cashews and pistachios are related, but they are distant relatives that come from distinct plants and produce very different fruit structures. Their connection is rooted deep within the plant kingdom, placing them together in the same overarching family. This shared botanical heritage explains why they have certain chemical and allergic properties in common, despite their obvious differences in appearance and taste.
The Shared Botanical Family
The relationship between the cashew and the pistachio is justified by their shared membership in the Anacardiaceae family, commonly known as the sumac or cashew family. This taxonomic classification indicates they share an evolutionary history, having diverged from a common ancestor. The family is recognized for its species’ ability to produce resinous or milky sap, which often contains irritating compounds.
Other notable members of this diverse family include the mango and the spice sumac. Perhaps the most infamous relatives are poison ivy and poison oak, which also belong to the Anacardiaceae family. The presence of these highly allergenic plants provides context for understanding potential irritants associated with raw cashews and pistachios.
Key Differences in Plant Structure and Growth
While botanically related, the fruits and cultivation methods of these two plants are fundamentally different. The cashew plant (Anacardium occidentale) produces a unique structure where the cashew nut is the true fruit, a kidney-shaped drupe. This drupe grows externally at the base of a swollen, fleshy stalk known as the cashew apple, which is often consumed fresh or processed into juice.
The shell surrounding the raw cashew nut is highly toxic and contains cashew nutshell liquid (CNSL), a caustic substance rich in anacardic acid. Specialized high-heat processing, such as roasting or steaming, is required to destroy these irritant compounds before the edible kernel can be safely extracted. The pistachio (Pistacia vera), in contrast, is a true drupe, a stone fruit where the edible portion is the seed inside a hard shell.
Pistachios grow in heavy clusters, and the fruit consists of a thin, outer, fleshy hull surrounding the hard shell. When the fruit is ripe, the shell naturally splits open along its sutures, which aids harvesting. The soft hull is typically removed soon after harvest to prevent staining. The pistachio tree is also dioecious, meaning separate male and female trees are required for pollination, a distinct difference from the cashew tree.
Comparing Nutritional Profiles and Allergy Risks
Nutritional Differences
The nutritional compositions of cashews and pistachios share the general health benefits of tree nuts but differ in their fat and micronutrient content. Cashews are notably higher in monounsaturated fats and are an excellent source of the mineral copper. They are also richer in magnesium, a mineral involved in processes like blood pressure regulation.
Pistachios contain a higher percentage of polyunsaturated fats, including omega-6 fatty acids. They are a superior source of fiber, containing more than triple the amount found in cashews, which aids in digestion and cholesterol management. Pistachios also boast a richer overall vitamin profile, providing higher amounts of B vitamins like thiamin and B6, as well as vitamin E and potassium.
Allergy Risks and Cross-Reactivity
The shared botanical family, Anacardiaceae, is directly linked to the potential for cross-reactivity in allergic individuals. People allergic to cashews are frequently co-sensitized to pistachios, and vice versa, because the nuts share several homologous allergenic proteins. These shared allergens include vicilin-like proteins and albumins that are structurally similar across both nuts. The presence of urushiol-like compounds, such as anacardic acid, in the shells of both nuts further demonstrates this chemical connection and contributes to the possibility of allergic reactions, particularly contact dermatitis.