Neem (Azadirachta indica) has at least two close relatives, A. siamensis and A. excelsa. They, too, are promising resources.
A. siamensis is known as ''edible neem" because its young leaves and flowers contain lower amounts of bitter principles than A. indica and are consumed in considerable quantities as a vegetable by people in Burma and Thailand. No negative consequences have been reported. A. siamensis also contains azadirachtin in its seed kernels and might be a useful source of pest-control materials as well as food.7
A. excelsa is a little-known tree of Southeast Asia. Recently, German researchers have isolated and characterized a new limonoid from its seed kernels. This compound, marrangin, shows the same mode of action as azadirachtin but is two to three times more active. Leaf extracts of A. excelsa also show a better efficacy than those of neem itself. 8