Vitex rotundifolia Seeds | Roundleaf Chastetree
LATIN NAME: Vitex rotundifolia
COMMON NAME: Beach Vitex
Plant Profile
Vitex rotundifolia grows on the front of the dune, where salt spray, wind and shifting sand remove almost everything else. It is a low, sprawling shrub with stems that run along the surface and root where they touch, forming a mat half a metre high and several metres across. The leaves are round, thick and grey-green, with a waxy surface that sheds salt.
The flowers are in short spikes at the ends of the shoots, a soft blue-violet with a lower lip marked in white, and they open through summer. The fruit is a small, hard drupe that turns grey and floats, which is how the species reached islands across the Pacific. It is native from Japan and Korea through southern China to Hawaii and Polynesia.
Science & Biotechnology
The leaf contains an essential oil dominated by rotundone, the sesquiterpene that gives black pepper its heat and also appears in some red wines. Vitex rotundifolia was one of the first plants in which rotundone was identified, and the compound is now used as a marker in flavour chemistry. The oil also contains pinene and limonene, and the leaf smells peppery when crushed.
The shrub is a classic pioneer of unstable ground. Its roots bind sand, its stems root from nodes, and its waxy leaves reduce water loss, so it can hold a dune face through a storm. That same habit makes it invasive where it has been planted outside its range: on the south-eastern coast of the United States it forms dense mats that smother native dune plants and block turtle nesting.
Uses & Benefits
In Chinese and Japanese medicine the fruit, called man jing zi, is used for headache, for eye complaints and for colds, usually in a decoction with other herbs. The leaf is used as a wash and the root as a tonic in local practice, and the plant appears in Japanese folk medicine for skin conditions.
The shrub is planted for dune stabilisation and as a ground cover on salt-exposed sites, and it is used in coastal gardens for the blue flowers and the grey foliage. In Korea the leaf is occasionally used to flavour food, and the fruit is burned as an insect repellent. The medicinal uses have not been confirmed in controlled trials.
Growing from Seed
Seed germinates slowly and unevenly. Soak it for a day, then sow in a sandy mix at 22 to 25 degrees; germination can take two to three months. Cuttings of semi-ripe wood in summer root readily and are the usual way to propagate a selected form, since the sex and the flower colour vary.
The plant needs full sun, sharp drainage and no rich soil, and it tolerates salt spray, wind and drought. It is hardy to about minus ten but resents wet winter ground, which rots the crown. Give it room to run, and do not plant it near a dune where it is not native, since it can spread and smother the local vegetation.
Our Take
A tough, salt-proof ground cover with a peppery leaf, and an invasive plant on coasts where it does not belong.
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