Carl Miller kindly sent in details of jambu and a link to Wikipedia. I had seen this defined as a type of cress and Wikipedia says: For culinary purposes, small amounts of shredded fresh leaves add a unique flavour to salads. Cooked leaves lose their strong flavour and may be used as leafy greens. Both fresh and cooked leaves are used in dishes (such as stews) in Northern parts of Brazil, especially in the state of Pará, often combined with chillies and garlic to add flavor and vitamins to other foods. A related species is used in several Southeast Asian dishes, such as salads. Consumption of portions or whole flowers have been reportedly used to offset the intense heat of chillies and peppers.
Eating a whole flower bud results in a grassy taste, followed by an extremely strong tingling or numbing sensation and often excessive saliva production and a cooling sensation in the throat. These buds are known as Buzz Buttons, Szechuan buttons, sansho buttons, and electric buttons.In India, the buds are used as flavoring in chewing tobacco.
Carl says that the numbing effect is similar to that when eating Szechuan pepper and he adds broken up buds to a shaker of gimlets or to gin and tonic. It can also be used as an analgaesic to reduce pain from toothache.