Cleistocalyx operculatus Seeds | Water Banyan
LATIN NAME: Cleistocalyx operculatus
COMMON NAME: Water Banyan
Plant Profile
Many myrtles hide their flower parts under a cap of fused sepals, but Cleistocalyx makes a speciality of it: the operculum covers the bud completely and is shed whole as a single lid when the flower is ready, leaving a clean circular rim behind. You can see that rim for the rest of the season, first around the open flower and then, as a dark ring, on the ripe berry.
The tree grows fifteen to twenty-five metres tall with a broad evergreen crown, and it is usually found within reach of water, along canals, streams and lowland watercourses, which is where its common name comes from. Leaves are opposite, oval to narrowly so, leathery and glossy, with a distinct marginal vein and translucent oil dots that release a resinous aroma when the leaf is crushed. Flowers are small and white to pale green, but each one carries a dense tuft of exserted stamens that gives the mass the brush-like look typical of the family, and they open in clusters on the older wood below the leaves rather than at the tips of the shoots. Bees work the display heavily, birds clear the fruit, and the berries ripen to a deep purple-black with the lid scar still visible on top.
Further north, the dried buds are one of the standard bitter ingredients in the cooling decoctions sold in the tea shops of Guangdong and Guangxi, simmered with other herbs such as chrysanthemum and honeysuckle and drunk when the weather turns humid. Because it tolerates wet feet and holds a bank with its roots, water banyan has also been planted along canals and streets across southern China for a very long time, and old specimens lean out over the water with their crowns meeting overhead. Its timber is hard and heavy and goes into construction and farm implements, and the flower clusters feed bees kept nearby.
Science & Biotechnology
The bitterness of the dried buds is chemistry you can taste. The compound most often cited from them is the chalcone recorded as 2′,4′-dihydroxy-6′-methoxy-3′,5′-dimethylchalcone, generally shortened in the literature to dimethylchalcone, together with related flavonoids and phenolic acids. It is this group that gives the bud infusion its bite and its staying power in the mouth, and it is the fraction that research groups reach for first.
Extracts of the flower buds and the pure chalcone both appear in published work on inhibition of alpha-glucosidase, the enzyme that trims starch into absorbable sugars, and in studies of antioxidant and anti-inflammatory activity. The leaves yield an aromatic oil dominated by monoterpenes and sesquiterpenes, and that oil, like the bud extracts, has been screened against bacteria and fungi. The bark carries tannins and has a separate history as a tanning and dyeing material in the region. None of that turns a table drink into a medicine, but it explains why the buds are collected seriously rather than casually.
Uses & Benefits
In northern Vietnam the fresh buds and young leaves are gathered into a basket and left to wilt and darken before they are brewed, and the transformation is not incidental: it softens the raw astringency and deepens the colour of the liquor. The result is a bitter, aromatic drink taken with meals through the hot months, poured from a jug rather than served as a remedy, and it keeps its character through a long steeping.
Growing from Seed
Clean the seed out of ripe berries as soon as they colour and sow it without drying, because its storage life is short. Use a free-draining mix of loam, coarse grit and leaf mould, cover the seed with about its own depth of compost, and keep the pan warm and lightly shaded. Prick the seedlings out as soon as the paired true leaves have opened, then grow them on in deep pots, since the roots resent crowding almost as much as they resent drying out.
Give the tree moist, well-drained soil and full sun, and water steadily through the growing season; it will take a wet site far better than a dry one, which is why it suits a pond margin in a warm climate. It is frost tender, so cool-climate growers should keep it in a large container moved into a warm, bright space before the first cold spell, and watch for scale insects and the sooty mould that follows them. Seedlings vary in habit, so anything wanted for a hedge or an avenue is raised from semi-hardwood cuttings rooted under mist, or from air layers on a chosen tree. Prune established trees only lightly, because the flowers and berries are carried on older wood inside the crown.
Our Take
This is a tree for a warm garden with water nearby, and the reward is a dense evergreen crown, a tufted haze of white flowers and a crop of buds you can dry for the teapot. Growers in the same family should look at the Hainan syzygium, a close relative of similar habit, and at the clove tree, whose aromatic buds are put to a very different use. The guava is the easiest myrtle to start with if you have never grown one from seed.
Related Reading
Gardeners who grow Water Banyan often pair it with these related subjects: