Vitex rotundifolia, the roundleaf chastetree or beach vitex, is a species of flowering plant in the sage family Lamiaceae. It is native to seashores throughout the Pacific. Its range includes continents and islands stretching from India east to Hawaii and from Korea south to Australia. This shrub typically grows approximately 1 m in height. It has a sprawling growth habit and produces runners that root regularly at nodes. This rooting pattern allows the plant to spread rapidly. At maturity, V. rotundifolia produces blue-purple flowers that are borne in clusters and ultimately yield small brown-black fruits. Its leaves are rounded at the tips with green upper surfaces and silver lower surfaces. While the plant is a seashore obligate, it grows over a wide latitude range. It has been used for medicinal purposes throughout its native range. More recently, it was imported to the eastern United States where it has become a seashore invasive. Control efforts are presently underway to protect the fragile beach dune ecosystem.
Description Vitex rotundifolia is a sprawling shrub that can grow as tall as 1.5 m though it typically ranges from 0.5 to 1 m in height. As a product of its rapid nodal rooting, the plant can form dense mats reaching in excess of 10 m from the parent plant.
Stems New stems are green, square and fleshy initially before maturing brown and woody. Older, large-diameter stems are covered with heavily fissured bark. Running horizontal stems produce frequent upright branches. Leaves are strongly aromatic, intensifying when crushed.
Leaves The majority of leaves are simple, but they can occasionally be palmate trifoliate or 2-leaved. Leaves measure 2 to 6.5 cm in length and 1–4.5 cm in width. Leaf margins are entire. The leaf shape varies from ovate to obovate with acute bases and obtuse apices. Occasionally, leaf apexes are acute or emarginate. Upper leaf surfaces are dark green whereas lower leaf surfaces range in color from silver to white to light green; all leaf surfaces are tomentose. Petiole bases are typically somewhat purple and measure 0 to 1 cm in length. Blades are cupped downward slightly. Leaf veins are lighter green than surrounding tissue.
Flowers The flowers are borne in indeterminate panicles that may be terminal or axillary. Inflorescences measure 3 to 7 cm in length. The calyx is cup-shaped and 4 to 4.5 cm long. Flowers are zygomorphic, purple to blue-purple, and short pedunculate. They are two-lipped and funnel-form (measuring 8 mm in length). Four stamens are didynamous and extend beyond the corolla tube (measuring 9 to 10 mm). The style extends beyond the stamens (total length: 12 mm). Pollen is tricolpate. Ovaries consist of two carpels with each containing two single seeded locules.
Fruits The fruits are globose drupes that are green while immature but turn yellow and red before maturing to bluish black. The fruits are frequently incorrectly characterized in the literature as "seeds or berries". Each drupe contains a maximum of four seeds though there are usually fewer as a result of seed abortion.
Seeds Each seed is encapsulated in a separate compartment. Endosperm is absent. Seeds germinate into tender seedlings that bear two cotyledons and quickly develop two red-margined true leaves. Ploidy level is 2n = 32, 34*.
Taxonomy Vitex rotundifolia is a member of the family Lamiaceae and subfamily Viticoideae. The plant was originally described by the son of Carl Linnaeus, Carl Linnaeus the Younger The original description was published in Supplementum Plantarum in 1782. The generic epithet, Vitex, is derived from the Latin viere, meaning “to bind or twist” in reference to the rope-like stems produced by some species in the genus. The specific epithet, rotundifolia, is derived from the Latin rotundus, which means "round, spherical", and folium, meaning "leaf.” This is a reference to the rounded character of the leaves.
Family level classification Vitex and all other members of the family Verbenaceae save those in the subfamily Verbenoideae were recently moved to the family Lamiaceae. As a result of this reorganization, two monophyletic families were established from the paraphyletic Verbenaceae and polyphyletic Lamiaceae. This new classification scheme was initially proposed by Cantino in 1992. Subsequent cpDNA analysis, rbcL sequence analysis, chemotaxonomic studies, and morphological analyses have supported the original logic for family reorganization. This revision has resulted in some confusion regarding the classification of V. rotundifolia in the literature. Despite the fact that the revision is well supported with volumes of data, many authors continue to incorrectly place the plant in Verbenaceae.
Species level classification Recent revisions of the genus Vitex have placed V. rotundifolia in synonymy with V. trifolia subsp. littoralis Steenis. Previous researchers have placed V. rotundifolia within V. trifolia. Moldenke (1958) placed V. rotundifolia in synonymy with V. trifolia var. simplicifolia. The placement of Moldenke was in disagreement with Corner (1939), which held V. rotundifolia as distinct from V. trifolia. The placement of Corner was subsequently supported by several authors: Fosberg (1962), Munir (1987), and Wagner (1999).
Common names
Likely due to the wide range over which V. rotundifolia is native, the plant has acquired a host of common names. English speaking countries
Beach vitex Round-leaved chaste tree Single-leaf chaste tree Chasteberry Monk's pepper China
Dan ye man jing Japan
Hamagou Korea
Sunbiginamu Man Hyung Ja(mainly medicinal name) Hawaii
Kolokolo kahakai Hinahina kolo Manawanawa Mawanawana Pōhinahina Polinalina
Hybrids Multiple hybrids between Vitex agnus-castus and Vitex rotundifolia have been developed at the Chicago Botanic Garden. These cultivars have undergone successful trials at Longwood Gardens. The characteristics of the hybrids are more like those of V. rotundifolia than V. agnus-castus. However, the hybrids are more upright than V. rotundifolia and have been described as "open and spreading." The leaf characteristics are intermediate between the two parent plants while the blue-purple flower color of the parents persists in the hybrid.
Distribution and habitat
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