Chaste tree (Vitex agnus-castus) in flower. The chaste tree grows up to 5 metres (about 16 feet) tall and can be maintained as a low shrub. The undersides of its five- to seven-lobed leaves and its branches are white felted. It bears spikes of small rose-lavender flowers arranged in whorls along the inflorescence. Vitex agnus-castus is the most common vitex used medicinally. The Vitex agnus-castus fruit, also known as chasteberry or monk’s pepper, is about the size of a peppercorn. It’s produced by the chaste tree, which acquired its name because its fruit was likely used to decrease men’s libido during the Middle Ages.