Rhamnus frangula Seeds | Alder Buckthorn
LATIN NAME: Rhamnus frangula
COMMON NAME: Alder Buckthorn, Glossy Buckthorn, Breaking Buckthorn
Plant Profile
The alder buckthorn spent two centuries filed under Rhamnus and has spent the most recent part of its history being moved out again. Philip Miller separated it as Frangula on the strength of characters that had always looked awkward inside the buckthorns: five-parted flowers instead of four, buds naked and without scales, and a shrub that never grows a spine. The genus name is the old Latin word for the plant, tied to the brittle quality of its wood. Later work on Rhamnaceae has backed Miller, though seed lists still print the Linnaean name.
The field characters that keep the two genera apart are easy to learn. Alder buckthorn carries its small greenish flowers in fives, its buds sit naked on the twig, its leaves have many parallel lateral veins that curve toward the tip, and its drupe holds two or three stones. Purging buckthorn has four-parted flowers, scaly buds, spiny branch tips and a fruit with four stones. Seen side by side, the separation Miller proposed looks less like a botanist’s whim and more like common sense.
Use the bark fresh and the result is violent griping and nausea, because newly stripped tissue is rich in reduced anthrones that act hard and fast. The traditional answer is time: strip the bark in spring, then let it dry and mellow for a year before it is powdered, by which point the anthrones have oxidised into the gentler glycosides. Every old herbal repeats the warning, and it is the most repeated instruction in the buckthorn literature.
Alder buckthorn is the great larval host of the brimstone, the butterfly whose adults outlive any other British species, sleeping through winter among ivy and emerging to fly on the first warm day of spring. Females lay their eggs singly on young leaves, and the caterpillars that hatch from them eat almost nothing else. The same shrub feeds the bees that work its small green flowers and the thrushes that strip the fruit, so a hedge with alder buckthorn in it is doing three jobs at once.
Science & Biotechnology
Frangula bark carries anthraquinone glycosides, chiefly glucofrangulin A and glucofrangulin B, along with frangulin and the free aglycones emodin, chrysophanol and physcion. The glycosides work as a prodrug. They travel intact through the upper gut and are split by the bacterial flora of the large bowel, which releases emodin anthrone; that compound drives colonic motility and pulls water into the lumen. It is the reason this bark acts low in the bowel, and why a tea of it is a different medicine from a bitter root taken to sharpen the appetite.
Uses & Benefits
This is a shrub of wet ground: carr woodland, fen margins, bog edges, the damp hollows of old hedges and the banks of ditches. It reaches five or six metres as a slender small tree with a neat rounded crown, its dark glossy oval leaves turning a soft yellow before falling. It flowers on the young wood through the summer and carries ripe fruit at the same time as the next crop of blossom.
The wood is pale, close-grained and dense, and in Britain the plant was coppiced on the fens and heaths under the name black dogwood for the charcoal it produced. That charcoal was prized for gunpowder, which needs a light, porous and hot-burning char, and the same material served artists as drawing charcoal. Handles and turnery took the rest of the crop, and the bark went to the apothecary.
Carried to North America as an ornamental and a wildlife plant, alder buckthorn has become a genuine problem in the wetlands of the American Northeast and Midwest, where it seeds heavily, spreads from root fragments and builds dense stands in fens, wet meadows and damp old pastures. Birds and floodwater move the seed, so control means cutting before the fruit colours, and then cutting again. It is a tidy lesson in how a hedgerow treasure in one country can turn into a thug in another.
Growing from Seed
Pick the black fruit when it is fully ripe and sow it at once, pressing each drupe into the surface of a gritty lime-free mix in a deep pan, then covering with five millimetres of grit and leaving the pan outdoors to take the winter cold. Thin the seedlings to five centimetres apart once the two-true-leaf stage has passed, then prick them out individually when four true leaves have opened. Water steadily rather than heavily, keep the frames shaded in the first summer, and plant the young whips out bare-root at forty to sixty centimetres tall for a hedge.
Our Take
If you are planting a wet hedgerow for wildlife, pair this species with the spiny, chalk-loving purging buckthorn, which shares the brimstone’s attention and suits drier banks in the same field. The American cascara is the genus’s other famous bark, and cascara buckthorn makes an interesting comparison for anyone studying anthraquinone chemistry. For a taller companion in damp ground, the Japanese raisin tree is worth a row, since Hovenia dulcis takes wet soil and gives an autumn display of its own.
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