Rhodomyrtus tomentosa Seeds | Downy Rosemyrtle
LATIN NAME: Rhodomyrtus tomentosa
COMMON NAME: Downy Rosemyrtle
Plant Profile
Downy rosemyrtle is a dense, suckering evergreen shrub of the myrtle family, usually one to two metres high, with opposite oval leaves that are glossy dark green above and softly felted beneath, which is what tomentosa refers to. The young growth is covered in a fine grey down, and the whole plant has the compact, bushy, slightly unruly habit of a shrub that spreads by underground stems as well as by seed.
The flowers are the reason it is grown. They are rose-pink to almost white, five-petalled, with a brush of prominent stamens in the centre, and they open over a long season in summer, singly or in small clusters in the leaf axils. In full flower a thicket looks as though it has been dusted with pink powder, and bees work it continuously from morning to evening.
The fruit is a small, round berry, green turning deep purple-black, with a thin skin, sweet, faintly resinous pulp and many small seeds. It is eaten fresh, made into jam, jelly and a sweet, slightly astringent wine, and it is one of the standard wild fruits of southern China and Southeast Asia, sold in markets in late summer and early autumn.
The shrub’s native range runs from southern China and Taiwan through Southeast Asia to India, in coastal thickets, hill slopes, roadsides and abandoned farmland, from sea level to about a thousand metres. It is a coloniser of disturbed ground and it forms dense stands on poor, acid soils, which is both its virtue and its problem.
Science & Biotechnology
The fruit is the subject of most of the modern research, and the findings are consistent. The deep purple colour comes from anthocyanins, with cyanidin and delphinidin glycosides well represented, and the fruit also carries flavonols, tannins and a high level of ascorbic acid. Extracts show strong antioxidant activity in vitro, and several studies have examined the anthocyanin stability under processing, which matters for anyone trying to make a stable juice or wine.
The genus is small, with Rhodomyrtus tomentosa as its best-known species, and it sits in the Myrtaceae close to the Australian and Malesian genera rather than to the temperate ones. The essential oil of the leaves has been characterised and is dominated by terpenes, with some antimicrobial activity reported, though the work is preliminary and largely from single laboratories.
Ecologically the shrub is a textbook bird-dispersed invader. The berries are eaten by bulbuls, mynas and starlings, the seeds pass through intact, and the plant establishes in disturbed ground, pastures and the edges of wetlands. In Florida and Hawaii it has become a serious problem in wet upland habitats, where it forms dense thickets, shades out the herb layer and alters fire behaviour. It is listed as a noxious weed in Florida, and management relies on repeated cutting and herbicide, because the soil seed bank persists for years.
Uses & Benefits
As a garden plant, it is best used as a flowering and fruiting shrub in a wildlife garden or a rough bank, where its suckering habit is an asset rather than a nuisance. It makes a decent informal hedge in acid soil, tolerates poor ground and salt wind, and flowers reliably in full sun. It is not a plant for a small, tightly planted border, because it spreads and because the birds will plant it everywhere.
The fruit is genuinely good to eat. It is sweet with a resinous, myrtle-like edge, best eaten fresh and warm off the bush, and it makes a dark, clear jelly because of its natural pectin. The wine is a traditional home product in southern China, sweet and low in alcohol, and the fruit is also used in preserves and as a filling for rice cakes.
The medicinal record is regional and modest. In Chinese practice the fruit is used as a tonic and the leaves and roots for diarrhoea and wounds, and the plant appears in the folk medicine of Thailand, Vietnam and Malaysia for similar complaints. Modern studies on the anthocyanins and on the antimicrobial activity of leaf extracts support some of this, but the evidence is not strong enough to treat the plant as a medicine.
For land managers outside its range, the useful message is caution. A plant that is a pleasant fruiting shrub at home is an aggressive invader in Hawaii and Florida, and it should not be planted near natural areas in warm, wet climates where it is not native.
Growing from Seed
Sow fresh seed, cleaned of pulp, on the surface of a loose, acid, free-draining mix, cover lightly and keep warm and moist at twenty-two to twenty-eight degrees. Germination is usually three to six weeks, and fresh seed germinates far better than stored seed, which quickly loses viability. The seed wants light, so a bare covering of compost is plenty.
Grow the seedlings on in full sun, in acid soil, and do not overfeed, since rich compost produces soft growth and few flowers. Plant out once the root has filled the pot, and water through the first dry season. The shrub suckers once established, and a thicket can be kept in bounds by mowing the edges or by cutting with a spade, but it should not be planted where that kind of containment is impossible.
Our Take
If you garden in a warm, acid-soil climate and want a shrub that flowers, feeds bees and gives you a crop of berries in the same season, this is hard to beat. Grow it where it can spread, pick the fruit before the birds take it all, and do not plant it anywhere near a natural area in the subtropics, because it has already shown what it does when it escapes.
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