Vitex agnus-castus -- Arizona

A live EDDmaps tracker hosted through Bugwood (2018) maps county occurrence of Vitex agnus-castus. The plant is shown occurring across the southern tier of states. Vitex agnus-castus generally occurs as a weed in wildland areas of the Southwestern Region rather than as an invasive plant (White, 2013). Vitex agnus-castus is showing invasive tendencies in areas where it has been planted extensively in landscaping, as in Texas (Bugwood, 2018). It is found in limestone outcrops and dry creek beds throughout Central Texas (Lady Bird Johnson Wildflower Center, 2006). The plant is listed by CABI Invasive Species Compendium (2007) under their "invasive" category for for Anguilla and Cuba and as "naturalized" for Brazil, Columbia, French Guiana, Guyana and Suriname.

Vitex agnus-castus has been noted as naturalized, or escaped from cultivation, in Arizona. The plant is mapped as naturalized in Maricopa, Gila, and Navajo County in Arizona (Bugwoodwiki, 2014). These occurrences are corroborated by SEINet, with additional occurrences in Cochise, Pima, and Yavapai County (SEINET, 2016). In Texas it has been found in limestone outcrops and dry creek beds throughout Central Texas (Lady Bird Johnson Wildflower Center, 2006) and this is a climate match with Arizona. However other sites consider the plant to be exhibiting no more than local weediness and state the plant can be safely used as an ornamental in all parts of Texas. They note the plant is not listed on the Texas Noxious Weed List (Texas A&M, 2022). Reports from Texas have prompted a suggestion that the plant be listed as an EDRR (Early Detection & Rapid Response) species across the southern United States where it is warm enough to survive the winters (Bugwoodwiki, 2014).

Appraisal of this species from the Southwestern USA suggest the species generally occurs as a weed in wildland areas of the Southwestern Region rather than as an invasive plant (White, 2013). Chastetree is a non-native species but is not considered invasive by the UF/IFAS assessment of non-native plants. Still, seeds may colonize nearby landscape beds and become weedy (Anonymous, 2022). Chastetree is certainly a weedy introduced exotic species in several regions, but there is not strong supporting evidence that its ecological effect is significant enough to be rated as invasive per the definition used by the PRE.

Vitex agnus-castus is documented as occurring in climate-matching regions of California, New Mexico, Nevada and Texas. Appraisal of this species from the Southwestern USA suggest the species generally occurs as a weed in wildland areas of the Southwestern Region rather than as an invasive plant (White, 2013).

Vitex trifolia is a naturalized alien new to the non-native flora of Tunisia and North Africa (Khalifa & El Mokni, 2020). This region is a similar climate, but the naturalization is not impactful enough meet the definition of invasive. Vitex rotundifolia is a more significant introduced species in the Southeast USA, but this is not in a similar climate (GISD, 2017).

Large areas of the native or near-native range of Vitex agnus-castus in Central Europe do not correspond with the climate match map for Arizona. Areas of establishment for the plant in Brazil and the Southeast United States also do not have a climate match. Southern Hemisphere regions with a climate match for Arizona have been little or not colonized by the plant (GBIF, 2022).

In Central Texas, it is reported to be outcompeting native vegetation (Lady Bird Johnson Wildflower Center, 2006). The PIER (2011) assessment lists the plant as forming dense thickets, but not having a climbing or smothering habit. Since the plant is a shrub or tree, this suggests it can overtop and shade smaller plants, but not in the manner of a vine.

Rated as not creating a fire hazard in natural ecosystems (PIER, 2011). However fire and the heat produced may induce higher seed germination (Travlos, 2007).

Vitex agnus-castus has effects on human physiology when consumed or applied in various ways. It has been used as a herbal medicine, and can have some adverse effects (Coon et al. 2005). However it does not appear toxic or poisonous in the conventional sense. The plant is rated as non-toxic but unpalatable to grazing animals (PIER, 2011). While unpalatable, the plant is not likely to be significantly displacing palatable forage, as it has been described as showing only local weediness. While it has been rated as forming dense thickets by PIER (2011), reports from individual states do not reflect this density on a landscape level of occurrence. The escaped occurrence of the plant has been most noted in Texas, but the plant is not listed on the Texas Noxious Weed List (Texas A&M, 2022).

The plant is a large multistem rounded shrub or small tree (White, 2013). Rated as forming dense thickets by PIER (2011).

Does not reproduce by vegetative fragmentation (PIER, 2011)

Does not reproduce by vegetative fragmentation (PIER, 2011)

Produces fertile seeds and readily seeds out into surrounding areas (Bugwoodwiki, 2014). Good seed crops occur almost every year, particularly in deep, moist soils along watercourses (PIER, 2011).

Yes, by inference, considering this can be a large woody plant producing many fruit. Numerous small flowers are produced on flower stalks up to 12 inches long. Each fruit contains four seeds. Seeds are small and and can average 40,000 seeds per pound (White, 2013).

In a test of Vitex agnus-castus seed germination under varying heat treatments, the control group exhibited a 68% rate of germination, with higher germination rates for heat-treated seeds (Travlos, 2009).

Vitex agnus-castus is a woody shrub or tree. It is rated as having a 3-year minimum generative time (PIER, 2011).

Flowers May to September (White, 2013). The fruits ripen in late summer and fall (PIER, 2011).

Fruit is a green and fleshy drupe, drying and turning brown, 1/8th inch in diameter. Persistent through the winter; containing four seeds (United States Department of Agriculture, 2013). Drupes presumably dispersed by birds & seeds therefore presumably survive passage through the guts of birds and/or other vertebrate dispersers (PIER, 2011).

Seeds or dry fruits containing seeds are noted to disperse by water, such as along riparian zones (PIER, 2011). By inference, this could be >100m.

Not considered a seed contaminant (PIER, 2011).