Vitex agnus-castus (also called vitex, chaste tree / chastetree, chasteberry, Abraham's balm,[1] lilac chastetree,[2] or monk's pepper) is a plant native of the Mediterranean region. It is one of the few temperate-zone species of Vitex, which is on the whole a genus of tropical and subtropical flowering plants.[3] Theophrastus mentioned the shrub several times, as agnos (άγνος) in Enquiry into Plants. It has been long believed to be an anaphrodisiac – leading to its name as "chaste tree" – but its effectiveness for such action remains unproven.[4]

Vitex is a cross-pollinating plant, but its self-pollination has been recorded.[5]

Vitex, its name in Pliny the Elder, is derived from the Latin vieo, meaning to weave or to tie up, a reference to the use of V. agnus-castus in basketry.[6] Its macaronic specific name agnus-castus repeats "chaste" in both Greek and Latin; the small tree was considered to be sacred to the virginal goddess Hestia/Vesta. The most common names are "chaste tree", "vitex", and "monk's pepper".[4]

Vitex agnus-castus is widely cultivated in warm, temperate, and subtropical regions for its delicately textured, aromatic foliage and butterfly-attracting midsummer spikes of lavender flowers opening in late summer in cooler climates.[7] It grows to a height of 1–5 m (3–16 ft). It requires full sun, though tolerates partial shade, along with well-draining soil. Under ideal conditions, it is hardy to −23 °C (−9 °F) USDA Zone 6.[8] In colder zones, the plant tends to die back to the ground, but as it flowers on new wood, flowering is not affected on vigorous growth in the following season.[9] This plant is a brackish water dweller, indicating that it tolerates salt. Cold and wet weather results in dieback and losses. The plant grows well on loamy, neutral to alkaline soil.[5]

In cultivation in the UK, the form V. agnus-castus f. latifolia has gained the Royal Horticultural Society’s Award of Garden Merit.[10][11]

The fruits from one single tree can be harvested for more than 15 years. This indicates that the tree cannot be integrated in a usual crop rotation system.[5][12] It is suggested to sow dissimilar plants such as monocots as its subsequent crop so that it might be easier to control the monk's pepper plant, the dicot. Because the fruits of monk's pepper tend to fall constantly and uncontrollably, the plant likely can germinate from seed.[5] The overall best yield per hectare reportedly can be achieved if the plant spacing is around 70 cm (28 in).[5] Pruning back the branches in autumn has a positive influence on fruit yield while repruning in spring can induce an increase of vegetative shoots, thus a fruit yield loss.[5]

This plant can also be reproduced vegetatively. One possibility is to use 5–8-centimetre (2–3 in) pieces of the ripening wood with buds in July or August and another is to cut the ripe wood in November and then let it root in a coldframe.[5] Also in vitro reproduction with spike of the shoots or node explants is possible.[13]

The flowering and ripening processes do not happen simultaneously, enabling harvesting of both fresh fruits and seeds over a long span of time. The fruits tend to fall from the plant as they ripen, getting lost in the soil. Thus, it has no optimal fixed harvest time. Consequently, to avoid yield loss, unripe fruits need to be harvested. This early harvesting has no effect on quality.[5] Overall, harvesting the fruits by hand likely is the most convenient solution.[12]

Thysanoptera, also known as thrips, can cause great damage to the growth and the generative development of V. agnus-castus.[14] The insect feeds on chaste tree by sucking up the fruit contents or puncturing them. Also, chaste tree is the only known host (especially in Israel) for Hyalesthes obsoletus. This cicada is the vector for black wood disease of grapevines. H. obsoletus prefers V. agnus-castus as a host to the grapevine. In this case, chaste trees can be used as a biological control agent by planting them around vineyards to trap the H. obsoletus.[15] V. agnus-castus was found not only to be an appropriate food source for the adult vectors, but also a reservoir of Candidatus phytoplasma solani (bacterial Phytoplasma species), the causal agent of the black wood disease in grapevines.[16] The pathogen-caused leaf spot disease can almost defoliate V. agnus castus. Furthermore, root rot can occur when soils are kept too moist.[17]

Flavonoids (vitexin, casticin), iridoid glycoside (agnuside, aucubin), p-hydroxybenzoic acid,[4][18] alkaloids, essential oils, fatty oils, diterpenoids and steroids have been identified in the chemical analysis of V. agnus-castus.[19] They occur in the fruits and in the leaves.[18]

Essential oils have been found in the fruits and in the leaves. The oil of leaves, unripe, and ripe fruits differ in compounds; 50 compounds were identified in the oil of unripe fruits, 51 compounds in the oil of ripe fruits, and 46 compounds in the oil of the leaves. 1,8-Cineole and sabinene are the main monoterpene components and beta-caryophyllene is the major sesquiterpene compound found in the fruits of V. agnus-castus. Some slight differences occur between fruits from white-flowering plants compared to violet-flowering ones. The oil of fruits of former has a higher amount of monoterpene constituents. The leaves mainly contain 1,8-cineole, trans-beta-farnesene, alpha-pinene, trans-beta-caryophyllene, and terpinen-4-ol. The oil, particularly from white-flowering plants, is under preliminary research for its potential antibacterial effects.[20]

Vitex has been used in traditional medicine for reproductive health issues in women, but no high-quality clinical evidence supports its effectiveness.[4][21][22]

Although vitex is commonly recommended in Germany,[23][24] V. agnus-castus should be avoided during pregnancy due to the possibility of complications.[4][23]

Adverse effects from Vitex can include nausea, headache, gastrointestinal discomfort, menstrual discomfort, fatigue, and skin disorders.[4][25] People taking dopamine-related medications or Parkinson's disease medications should avoid using chasteberry.[26] Women on birth-control pills, hormone-replacement therapy, or having a hormone-sensitive condition, such as breast cancer, are advised not to use chasteberry.[26] Use of Vitex is discouraged for pregnant or breastfeeding women, and for children.[4]