Rosa rubiginosa Seeds | Sweet Briar
LATIN NAME: Rosa rubiginosa
COMMON NAME: Sweet Briar
Plant Profile
The shrub is a dense, arching, prickly thing that reaches two metres and more if left unpruned, with small, glossy leaves in fives and sevens and single, cupped pink flowers with pale centres through early summer. It is the traditional eglantine of the hedge and cottage boundary, grown exactly where people brush past it, and the one rose whose foliage is worth more than its bloom.
The hips are oval, red and borne in clusters, and they ripen in autumn. Their value is ascorbic acid, which the hip wall carries in quantity. During the Second World War, when citrus imports were cut off, Britain organised a national collection of wild rose hips, with schoolchildren paid by the pound to gather them from hedgerows, and the hips were processed into syrup issued to children as a vitamin C source. They are still used for jelly, syrup and tea.
The vitamin sits in the fleshy wall rather than in the hairy seed at the centre, so the traditional method is to stew the hips and strain the pulp through a cloth. The irritant hairs around the seed are the reason for that caution.
In south-eastern Australia and New Zealand, sweet briar is a serious weed of grazing land, forming dense, thorny thickets that take grazing out of production until they are cleared. Birds and possums spread the hips into pasture and along fence lines, and the caninae genetics that makes the seed come true to the mother makes the seedlings consistent and vigorous. In both countries it is a declared or managed pest plant.
Science & Biotechnology
The leaves, leaf stalks and young stems carry short-stalked glands, and each holds a small droplet of volatile oil under a thin cuticle. Touch the plant and the heads break, and the oil is released into the air at once, which is why the scent arrives in a rush from disturbed foliage and fades when the plant is left alone. The same arrangement gives mint, thyme and the scented pelargoniums their aroma.
Sweet briar belongs to the dog rose group, and the dog roses have a genetic system unique among plants. They are odd-numbered polyploids, sweet briar being pentaploid, and their meiosis is unbalanced: only seven pairs of chromosomes form bivalents and divide normally, while the rest pass to the egg cell as unpaired units. The seed parent therefore contributes most of the chromosomes and the pollen few, so the offspring resemble the mother almost completely.
Uses & Benefits
The same plant that is a nuisance in one country is a crop in another. In Chile, where it naturalised long ago, sweet briar is harvested for its seed oil, pressed and sold to the cosmetic industry as rosehip oil; the oil is rich in linoleic acid and carries small amounts of trans-retinoic acid. It is a reminder that a weed is a plant in the wrong economy.
Growing from Seed
That asymmetry has a practical consequence: sow hips from a good sweet briar and most seedlings come up looking like the parent, which is unusual for a wild rose. The pollen is genetically uniform, so the species behaves in the field as though it were cloning itself through its seed.
Rose seed is dormant twice over: the embryo inside the hard achene is immature at fruit fall and needs a warm period to finish developing, followed by a cold one to break the coat. The simplest treatment is to clean the seed from the hips, mix it with damp sand, keep it warm for a season and then cold through a winter, then sow it in a pot outdoors under a cover of grit. A cold frame suits it better than a windowsill, and the seed can take more than one winter.
Sweet briar flowers on the previous year’s wood, so prune after the flowers fade and not in winter. Take out some of the oldest canes at the base, shorten the rest by about a third and keep a stem count that lets air through, since a congested plant is a mildewed one. It suckers from the roots and makes a thicket if given room, and it shrugs off drought, poor soil and cold.
Our Take
I grow it at the gate, where every visitor squeezes past and the whole point of the plant is proved on other people. Give it sun, poor soil and no pampering, and it will make a scented hedge that survives neglect. Dog rose has the same hips and the same canina genetics without the scent, rugosa rose is the thorny windbreak rose for a harder site and a bigger hip, and hawthorn is the hedge shrub I plant with it when the boundary needs to be stock-proof. Plant it where people pass, and cut it back after it flowers.
Related Reading
More species in the same orbit as Sweet Briar: