China, Japan, and India
Vitex rotundifolia is considered an invasive species in the Carolinas and has the potential to spread to many more coastal communities along the shores of the United States (Madsen,et al, 2005). Beach vitex is a rapidly growing and sprawling shrub both vertically and horizontally that is very tolerant of salt and drought (Gresham & Neal, undated). Beach vitex produces a large seed bank and can reproduce vegetatively through rooting at leaf nodes along runners (Gresham & Neal, undated). The impact of its aggressive growth pattern leads to little light reaching the soil surface where it dominates as monocultures preventing native species from establishing (Gresham & Neal, undated). In addition it has been suggested from scientific observations that the plant releases some allelopathic compounds that have actions in the soil to make it hydrophobic, causing drought stress to less tolerant native species (Gresham & Neal, undated).
Vitex rotundifoliais a branched deciduous shrub (Westbrooks and Brabson, 2007) that can reach heights between 0.5-1 metres and have horizontal growth up to 20m long, but more commonly has a width around 5 metres (GRI, 2006). According to Westbrooks and Brabson (2007), the "branchlets are obscurely tetrangular, tomentose, stems procumbent, often rooting at the nodes, forming mats several metres in diameter, 1-3dm long". The leaves are simple obovate to suborbicular, 2-6.5cm long, 1-4.5cm wide, and an acute base. The upper surface of the leaf is pale green and densely puberulent with a greyish-white lower surface. The lower surface of the leaf is also densely tomentose, short petiolate, and apex rounded (Westbrooks and Brabson, 2007). The foliage has a spicy fragrance when crushed (HNPPD, 2001). The flowers are arranged in terminal clusters in panicles, and about 2cm long (Gresham & Neal, undated; HNPPD, 2001). The corolla is bluish-purple, densely puberulent externally, with the tube about 8mm long. The upper two lobes are 3.5mm long with the margins recurved. The lateral lobe is about 4mm long and the lower lobe is about 7mm long. The base of the lower lobe is marked by two white pilose. The stamen is esxerted from the corolla. The filaments are 9-10mm long and pilose at base. The style is also exserted from the corolla and is about 12mm long. The fruit consists of a dry, globose drupe, and is about 6mm in diameter. During September-October the fruit turns from green into yellow and red-tinged. At maturity the fruit is bluish-black (Westbrooks and Brabson, 2007).
Vitex rotundifolia is an obligate sand dune species (Kim, 2005). It is found at low elevations on beaches, sand dunes, and rocky shorelines (HNPPD, 2001). Beach vitex is highly salt and drought-tolerant (GRI, 2006) and grows best in full sun and sandy or well-drained soils (SCNPS, undated).
Vitex rotundifolia was introduced to the southeastern United States from Korea by North Carolina State University Arboretum in the mid-1980s. It was introduced for the purpose of dune stabilisation and for ornamental use(Westbrooks and Brabson, 2007).
Has been reported in the Florida counties of Santa Rosa and Escambia.
Mechanical: Hand-pulling, digging, and the use of machinery are all options that can be used to remove beach vitex, however due to the fragile nature of the dunes and the risk of erosion these methods should be used with caution (Gresham & Neal, undated; SCNPS, undated). Chemical: Several different techniques of herbicide application are being tested on beach vitex. Three different techniques can be used to apply a herbicide to the plant. One method is to cut the aboveground vegetation back to a stump and then apply a glyphosate paint to the exposed cut (Sea Grant NC, 2006; Grisham, undated). The second method is to wound the stem and then apply a herbicide to the wound (Sea Grant NC, 2006). The third method is to apply an oil based herbicide mixture to the stem in a 30-45cm length band at the base of the stem (Sea Grant NC, 2006).
Photos courtesy Forest and Kim Starr, licensed under a Creative Commons Attribution 3.0 License.